Calling all insulation geeks! (XPS vs. Polyiso, etc.)

[Vagabound]

(If what I'm asking has been covered sufficiently, just direct me to the thread please.  Though there were a couple mentions, I didn't find one while searching)

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Hi,

Unless somehow crucial, let's leave EPS (white coffee cup styrofoam) out of this discussion.  Just don't want to muddy the waters unnecessarily.

It wasn't until I started reading threads here on CRVL that I heard of polyiso foam boards (or else I'd forgotten).  Up to that point, XPS foam was the best choice.  However, people here seem to be promoting polyiso more.  I'd like to know why.

" Calling all insulation geeks! " ;-)​

1.  R-Value:  
I know that polyiso has a somewhat higher R-value than XPS.  Depending on which source you consult, the difference is roughly XPS at 5.0 and polyiso at 6.0.  I'll stick with those numbers for easy math.  However, even without being an insulation engineer, those numbers are not very useful unless we know if the R-value scale is linear or exponential / logarithmic.  For those of you wondering why anyone would care, the answer is the difference between a) a little better, and b) many times better.  And that's a huge difference.

In other words, is 6.0 only 20% higher than 5.0 (linear) on the R-value scale,  or is it twice or four times or 10 times higher (exponential / logarithmic ... like earthquake measurements).  I have searched online for this answer and could not find it.  I suspect it is simply linear (20% in this case).  If anyone knows the answer, I'd would really like to know.  Bonus points to anyone who can also provide a source to back up their answer. 

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2.  XPS vs. Polyiso - The Cage Match
Seriously, is polyiso really better overall?  Based on what I've read, I don't think so.  While polyiso has a bit better R-value (maybe - answer to Q1 is pending), it is harder to work with, off-gasses a lot, and so loses some of its R-value, and tends to get brittle over time and deteriorate, according to some people.

So, in the opinion of the collective brain trust here, what would a pros and cons list for each product look like?  And in the end, for vandweller applications, which one factually wins and why?

Thanks,

Vagabound

 

[Vagabound]

38 views and 0 replies so far.  Not too common here.  That says something, but not sure what yet.  Hmm ...  Still, I realize it's not an easy question.  

Vagabound

 

[Almost There]

Well, let's see - I think the  number of views with no answer has something to do with there being no 'insulation geeks' around....  

Here's the Wikipedia explanation of R values:

https://en.wikipedia.org/wiki/R-value_(insulation)

It made my head spin and my eyes roll to the back of my head but have at it....  

And a simple non geeky answer to the question would be - if you can use something that fits and has an R value of say 6 and it's cost effective, why would you use something that has an R value of 5. I don't need to know the technical side of how R value is measured to know that the higher number (if at app. the same cost) would be a better deal!

 

[AuricTech]

Well, according to The Font of All Human Knowledge, R-values for typical materials are additive, which indicates a linear scale.

ETA: The linked table is for R-values per inch of material.

As Almost There pointed out, the hows of calculating R-values can by complex. The table to which I linked boils it down to what you probably need to know about using R-values in general.

 

[BradKW]

Wish I could remember the old thread from the fellow that wanted to use thousands of dollars of some vacuum sealed NASA-type insulation panels...that was an amusing one.

Anyway, short of stuffing old clothing and newspaper into cavities, there's no right or wrong answer. If I told you that 2-part spray foam would give you the best of all worlds, 3 people would explain that spray foam is evil and will rust your van away inside a month...which won't matter since you'll have dropped dead from outgassing anyway.

I'm actually using foam, XPS and Poly ISO...just go with what makes sense to you. If using Thinsulate tied to fish tape to thread it through the columns sounds like a worthy way to spend a Sunday, by all means do it...twice

 

[DannyB1954]

One thing it is flammable. Other foams will burn, but usually only if a flame is held to them. Take the outside flame away and they will usually extinguish. Styrofoam once started on fire will burn until it is consumed.

 

[Vagabound]

Well, let's see - I think the  number of views with no answer has something to do with there being no 'insulation geeks' around....
...

Best point made so far.  Might be the case, but it would surprise me.  Lots of people know some surprising things about the most unusual or specific topics.  But it does lead me to guess that the engineer-vandweller population must be very small.

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I normally wouldn't mention this, but I've noticed that it seems to be a trend, rather than a single instance.  Not pointing to anyone in particular, nor only to this thread or forum for that matter.  

Something in reply psychology often takes me by surprise.  And it shouldn't still, after all these years.  Guess that says something about my inability to adapt.

Typically, when questions are posed that people don't know the answer to, you get a pretty clear split into two groups of people replying.  

The first group reads, realizes they don't know, and stays quiet, or replies and says "I don't know, I hope someone else can answer your question.  Best of luck."  

And then there's the second group.  Ah, the second group.  They also don't know -- and that's a key point.  Even though they don't know the answer, they feel oddly compelled to reply.  But with nothing to really contribute, not even simple well-wishes, their reply typically follows one of these formats:  the question isn't valid, no one cares, no one needs to know, or that the question is too __[fill in the blank]__, etc.  

However, their reply was never intended to be helpful.  It was intended to belittle the person who asked the question.  I guess no one ever explained to the beloved second group people that such a method is the oldest, and most obvious way of trying to cover up ignorance in order to feel and appear equal or superior regardless.  

I don't know it if works for the person doing it, but it surely doesn't move conversations or knowledge forward.  And it's kinda silly in the first place because we're all ignorant of many, many things, and always will be, and so, it isn't something to automatically feel bad about or to dodge or to hide.

Maybe we can do more to support the first group and discourage the second.  In any case, something we could ponder before we next click the "Post Reply" button.

Vagabound

 

[BradKW]

Kinda feeling like that was directed towards me, so let me just say that you might consider the possibility that were a person, hypothetically, getting stuck on a bit of overanalysis, they might also misinterpret a little wisdom as perhaps being snarky.

Having spent rather absurd amount of hours over analyzing insulation options myself, and reading countless discussions in various forums, as well as installing insulation and spray foam professionally for decades, I can discuss it ad nauseum. My advice to you was actually meant to be helpful, as it represents what my cumulative opinion on the subject now boils down to.

I apologize if it made you feel talked down to, that wasn't my intention. But I do see how it could be read that way.

edit: oh, and the thread I referenced was amusing, but it was also an had some very good discussion in it so I was hoping someone links it. I thought the guy was a bit nuts to spend that type of money, but he actually knew some pretty esoteric insulation information

 

[Vagabound]

Kinda feeling like that was directed towards me, so let me just say that you might consider the possibility that were a person, hypothetically, getting stuck on a bit of overanalysis, they might also misinterpret a little wisdom as perhaps being snarky.

Having spent rather absurd amount of hours over analyzing insulation options myself, and reading countless discussions in various forums, as well as installing insulation and spray foam professionally for decades, I can discuss it ad nauseum. My advice to you was actually meant to be helpful, as it represents what my cumulative opinion on the subject now boils down to.

I apologize if it made you feel talked down to, that wasn't my intention. But I do see how it could be read that way.

Brad,

Thanks for saying so, and for clarifying.  Overanalysis reaction: Could be onto something there. Your new version was helpful, as is your first version now, considering all of your knowledge on the topic. Though there might have been a bit of the camel/straw/broken-back thing going on, I really did mean what I said at the beginning:

I normally wouldn't mention this, but I've noticed that it seems to be a trend, rather than a single instance.  Not pointing to anyone in particular, nor only to this thread or forum for that matter. 

I just get annoyed when I'm trying to solve something, and instead of help or silence, I get people rushing to provide rocks to step over.  When that happens, at first, I tend to ignore the rocks and hop over them.  But at some point, I turn around, squint, and start walking back toward the rock guy.

Maybe my attitude partly comes from an old military saying:  Lead, follow, or get the hell out of the way*.

Thanks,

Vagabound

P.S. - * Or at least tell a joke.  Wait, a post from Brad without a joke.  Hurry!  Someone call the doctor!  ;-)

 

[Vagabound]

Well, according to The Font of All Human Knowledge, R-values for typical materials are additive, which indicates a linear scale.

ETA: The linked table is for R-values per inch of material.

As Almost There pointed out, the hows of calculating R-values can by complex.  The table to which I linked boils it down to what you probably need to know about using R-values in general.

AT,

Where in TFOAHK are you getting that "additive" part?  Looked but didn't see it.

Vagabound

 

[AuricTech]

Vagabond,

Since the table covers typical R-values per inch of material, adding an inch of material would add that material's R-value.

Let's use high-density XPS (HD XPS) as an example. The table gives an R-value range per inch of R-5 to R-5.4. So, adding 2" of HD XPS to the wall of a metal shed would provide R-10 insulation. Adding two more inches of HD XPS would give us R-20 insulation.

Meanwhile, if our shed had 1" hardwood walls, that 2" of HD XPS should (assuming no air space between the wall and the insulation) give a total R-value of R-10.71 (2" of HD XPS @R-5 per inch, plus 1" of hardwood @R-.71 per inch).

That's what I meant by "additive"; perhaps I should have used the term "linear."

Does that clarify things?

 

[PedalFlyer]

So I'm not sure which group you want to put me into, and at this hour I could give a rats butt, but here is some input for a guy who was an insulation rep, and outfitted a number of companies insulation fleet (yup, I've been a truck guy most of my life too).  I'm not engineer, but if I had a buck for ever engineers who butt I rescued because even after all their over analyzing everything, they still got it real wrong, I'd be a rich man today. 

So, spray foam...not the best idea for reason of trapping moisture, but you could spray with a barrier and overcome that obstacle, but then there is the off gassing.

Any of the foam boards are options, except they leave gaps between the surface and the product and that is not good for space utilization, or thermo-dynamic efficiency.  Plus as noted, some of them will break down over time, others due to temperature exposure and so on.

Air-trap or wrap, low R value and limited life span.

So.....what to use....how much money and time ya got?  I could write a book filled with possibilities. 

There is a product on the market called Aeroseal....its not inexpensive and its not insulation, its an airsealer.  Have the inside of the van coated, than template or prepare your walls for mounting and leave plug-able openings in each "bay" of the van that you will be covering and want to insulate.  Then choose, between dried foam insulation, lambs wool insulations (yes I know this will trap moisture, but its "wool" hence it will shed the moisture in the natural cycle of heating and cooling and with the aerosol serving as a barrier, it will not effect the sheet metal.  You could also consider blown in denim or a host of other material as well.  The R values to these materials depends on the efficiency they are "packed" into the cavity with.  You can however build a very high and sustainable R-Value.  They don't off gas. They will deaden sound from the outside, inside and from the vehicle itself.  Some will add a lot of weight, but others nearly none. 

The vast majority of vehicles I've watched or seen or actually done have been poorly insulated and even when "no expense" was sparred or the highest and best material was used, the reality is, insulating a vehicle is not a simple task.  Using thin or low R-value material on the floor is just ignorant.  The cold air, and colder air radiating from the ground is going to reach the outer floor of the van, and then once it sufficiently cools the bottom of the vehicle, it will conduct that cold to the rest of the sheet metal, and then the thermodynamics kicks in with reaching the material inside the vehicle.  So the best insulation is the insulation that is barrier protected from the sheet metal of the vehicle, and then uses pockets of air and non-thermoconductive materials to insulate the truck. 

I'm sure you'll have fun taking issue with this, but its reality.  Before you rip it or me apart, think about it.  You might start to see some of the points I'm suggesting, if not, oh well. 

I do hope this helps you.

 

[Vagabound]

...
That's what I meant by "additive"; perhaps I should have used the term "linear."

Does that clarify things?

You explained very well how you were using the word "additive" and all of it makes perfect sense to me.  Thanks.  Unfortunately, it isn't related to the question that I was originally asking, so that's still pending.

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For anyone still trying to help answer or learn, like me, let me try this again as briefly as I can.  An example might help:

Earthquakes.  Richter scale measures/rates them.  4.0 on the Richter scale, etc.  We all know about that.  What we don't all know or think about is this ... on that scale, a 5.0 earthquake is not 25% stronger than a 4.0 earthquake.  It is 10 times stronger.  Every increase of 1.0 on the scale is x10.  In the words of someone who knows:

Magnitudes are based on a logarithmic scale (base 10). What this means is that for each whole number you go up on the magnitude scale, the amplitude of the ground motion recorded by a seismograph goes up ten times. Using this scale, a magnitude 5 earthquake would result in ten times the level of ground shaking as a magnitude 4 earthquake 

http://www.geo.mtu.edu/UPSeis/intensity.html

So, the earthquake strength scale is logarithmic (x10).  Other scales, like your weight in the gym, are linear.  200 lbs is 25% more than 160 pounds.  161 pounds is not 10x more than 160 pounds.  If it were, it would be logarithmic.  Different scales measure things in different ways.

All of that above is only important to understand the question I actually asked about R-values vs. all this other stuff that has muddied the water.  Believe it or not, it actually applies to R-values.  And anyone who doesn't understand that, doesn't understand R-values yet.

Moving on ...

(PedalFlyer)
I'm not engineer, but if I had a buck for ever engineers who butt I rescued because even after all their over analyzing everything, they still got it real wrong, I'd be a rich man today. 

Yeah, yeah.  Heard it all before ... every officer in the military couldn't find the bathroom without the sergeant, and every doctor, without the constant supervision of the nurse, would be sitting still, lost and drooling.  In a pig's eye.  ;-)

So I'm not sure which group you want to put me into, and at this hour I could give a rats butt, 
...
I'm sure you'll have fun taking issue with this, but its reality.  Before you rip it or me apart, think about it.  You might start to see some of the points I'm suggesting, if not, oh well.

 
Interesting how this has all been turned around backwards.  I asked two questions, people can't answer, so they say unhelpful things or deflect the topic, and when I call them on that, magically, I'm the problem.  SSDF.

Despite you jumping to some wrong conclusions about what my intentions are, apparently without trying to understand them, I do sincerely appreciate you adding some info to this thread, especially considering your extensive experience with insulation.  However, it pains me to say that your answer is also unrelated to the questions that I asked.  I did not ask for general insulation recommendations.  In fact, I specifically asked to avoid that.  Instead, I asked for something very specific, explained in Post # 1.  And no, that wasn't fun.  It was just necessary.

I do hope this helps you.

And I hope you sincerely mean that.


I'm really stumped by the confusion and off-topic reactions to two questions very clearly stated.  

I'm not trying to get a degree in materials engineering or prove I'm some smarty pants.  It should be self-explanatory that someone who admits they don't know something (me) and asks for help (me), isn't trying to demonstrate superior knowledge in that area.  

If someone else wants to demonstrate their individuality or eccentric personality, and wants to stuff their van walls with elephant dung or used chewing gum, fine.  I'll probably watch, laugh, cheer them on, drink a beer, and have a good ole time.  But that's not me.  I'm actually trying to learn this stuff, in order to make good decisions about insulation.  Saying that I'm "over-analyzing" this is just more deflection.  If someone had posted the actual answer in Post # 2, or Post # 3, this could have been a very short and effective thread.  That didn't happen.

So, please, if you (anyone) doesn't know the answer, fine.  Don't give one.  On the other hand, if you know the answer, fine, please give it, or otherwise reply if you have something on topic to add.  

I would appreciate that, but it is probably best not to assume you know my intentions other than what is plainly written and explained in my posts (something that I struggle to do towards others as well).


To restate my original questions, I just want to know: 

1.  What different R-values mean, in relation to each other (R-5 vs R-6, etc).  Sure, an R-3 thing added to another R-3 thing is R-6, but that still doesn't explain how much stronger (effective) R-6 is than R-5.  Are R-values like the earthquake scale or like the weight scale in the gym?

Ideally, I'd like to find (or someone else to find) a short explanation of comparative R-value strength similar to the example that I provided above about earthquakes from Michigan Tech.  That would settle the issue and give anyone who wants to actually understand R-values the info they need.

2.  How do XPS and polyiso compare, and why are so many people hip on polyiso?  

That's it.  Nothing more.  Let's turn this mountain back into a molehill.

Thanks,

Vagabound

 

[AngryVanMan]

R-value (US) is (ft²·°F·hr)/Btu - a simple linear value of thermal resistance, and is the reciprocal of thermal transmittance - U-value. The original source is ASTM C168, but if you don't want to spend $50 to read it, the Wikipedia page is a decent proxy. Easy enough answer for section #1, the 20% difference in the example given is apt.

XPS vs. PolyIso
Which is better "overall." Well that's a fun question with an obvious objective answer surely.

As insulation, new PolyIso is better than XPS (higher R-value). Aged PolyIso is better than XPS, maintaining a higher overall R-value as well. They are very similarly priced. It follows that, as insulation, PolyIso is better.

Easier to work with. They both are foam boards you cut with a knife and stick in place with adhesive or fix with wall sandwich components. Both are used regularly by construction workers with no special training, I can't really speak to a measurable level of difficulty here. I would have to compare this to the nuance of difficultly in spreading the peanut butter or the jelly. Peanut butter is smoother spreading and XPS is slightly more flexible, but an able-bodied child could manage both in the "field" so to speak.

Off gassing. Eh OK. All plastics, paints, glues off-gas but there are no concerns listed on the MSDS for either of these post-installation. XPS contains HCFC gasses and PolyIso's I looked at contain either HCFC or pentane gasses. Deeply concerned individuals would be better served working out a well designed ventilation system and/or careful selection of products they come into skin contact with on a daily basis.

Physical Deterioration. Don't excessively attach or fix rigid materials to flexible structures. Don't use non-load bearing products under loads or for weight bearing. This is an "engineering" problem that can be addressed in situ. PolyIso is more rigid of the two choices, so it could be easier to ham-fist the install of the less forgiving product.

Which wins? Usually I pick the best insulation because it is the best insulation and I want the best insulation for energy and comfort reasons, which in this case between these two products would be the PolyIso foam board. If I was unable to deal with the nuanced difference in the physical properties of the best performing product, then I would pick the second best, and so on down the line until I found a product I liked that was also within my skill to apply and fit the application. I'd say it's objectively subjective. PolyIso is objectively better performing insulation of the two. High density XPS is what I would use on a load bearing floor.

 

[Vagabound]

R-value (US) is (ft²·°F·hr)/Btu - a simple linear value of thermal resistance, and is the reciprocal of thermal transmittance - U-value.  The original source is ASTM C168, but if you don't want to spend $50 to read it, the Wikipedia page is a decent proxy.  Easy enough answer for section #1, the 20% difference in the example given is apt.

XPS vs. PolyIso
Which is better "overall."  Well that's a fun question with an obvious objective answer surely.

...

Which wins?  Usually I pick the best insulation because it is the best insulation and I want the best insulation for energy and comfort reasons, which in this case between these two products would be the PolyIso foam board.  If I was unable to deal with the nuanced difference in the physical properties of the best performing product, then I would pick the second best, and so on down the line until I found a product I liked that was also within my skill to apply and fit the application.  I'd say it's objectively subjective.  PolyIso is objectively better performing insulation of the two.  High density XPS is what I would use on a load bearing floor.

AngryVanMan,

I felt it in my bones.  I knew there was someone out there in the electronic wasteland who knew the answer!

Thank you for paying attention to what I was actually asking and for being detail-oriented.  You might be an "angry man," but I'm sure not!  That was a really fantastic answer!  Basically what I've been waiting on since the beginning of the thread.  I understood everything (except the math formula).  But all the ideas and explanations and conclusions - check.  I feel compelled to hug you, but, deferring to the rules of machismo and strangers, if we ever meet, the first beer is on me.  

You strike me as a person who can handle a question or clarification without losing his ****.  So, I'll risk it.

1.  You said, "As insulation, new PolyIso is better than XPS (higher R-value). Aged PolyIso is better than XPS, maintaining a higher overall R-value as well. They are very similarly priced. It follows that, as insulation, PolyIso is better."  You seem to limit the definition of "best" to solely highest R-value.  Is that perhaps too limiting, needing to be expanded by including some other factors before totaling to "best", or just the only factor worth really considering in your opinion?

2.  You said, "PolyIso is more rigid of the two choices, so it could be easier to ham-fist the install of the less forgiving product."  Lost me here.  Your conclusion doesn't seem to match the beginning of the sentence.  I would have finished your sentence with "more forgiving".  What am I missing?

Although the math probably speaks for itself, maybe someone will run across an authoritative online source saying simply what you said -- the R-value scale is linear.  If not, I'm OK with that.

That's all I really wanted -- someone who knows what he's talking about to help me think about this a little bit.

Thanks again for a great reply.  

Vagabound

 

[Trebor English]

The last time I went to Home Depot to buy insulation I got polyiso.  It was the only foam they had that day.  Sometimes unexpected issues sway the decision.

 

[anewbiewannabe]

One thing it is flammable. Other foams will burn, but usually only if a flame is held to them. Take the outside flame away and they will usually extinguish. Styrofoam once started on fire will burn until it is consumed.

Which one is styrofoam---XPS or polyiso? or were you talking about the coffee cup?

Thanks!

 

[PedalFlyer]

Okaay....lets try this again.  Since I am apparently being accused of being a bone head, let me see if I can take the excellent answer offered by AngryVanMan and take things a step further to assisting you in your quest for the best resolution.  BTW, my comments were intended not to inflame you, but to address the reality that there really is no one best answer.  But, perhaps this will help you find your own best insulation. 

So, to clarify: R-Value is used to measure thermal resistance of structure.  Structure can be any material, any "constructed" vessel from a pipe, to a house, to a van or RV. 

Now its also been written here that R-value is the opposite of U-value, or more commonly known as U-factor.  So...U-factor is similar to the K-value, but U-factor gives the amount of HEAT that transmits through a square foot of a structure (building, van, RV) cross section composed of multiple slabs of material.  So in our illustrative case, it would be the sheet metal of the truck, some sort of barrier material, and the insulation itself and whatever is used for the "wall".  '

So think of the R as symbolic for Resistance, not like weight in a gym or earthquake scale.  Its how much air movement can you throw at it, verse how much of that air will penetrate it to the other side.  The difference is the resistance or the R value.  So a R 5 is not as good as an R 6.  As an example we used to recommend homes in the northeast be insulated to a R-15 value...today its suggested R-30+++.  Same with the RV industry.  They used to insulate to a R-3 or 4.  Todays "winter performance" packages take it up to an R-8 or better.  

Here is the issue I was not being clear about at 3:am.  People, not just you, people in general focus to much on R-Value and so on.  The real concern is staying warm or cool, right? Right.  So what you really want to look at is: Heat Load.  That plus ACH or Air exchanges...which is why I mentioned air sealing in my original answer. 

So...to calculate heat load you would do the following: U-Factor is the inverse of R-Value, meaning that: U = 1/R and R = 1/U.  Since U - Factor is the inverse of R-Value, when R=1, U=1; when R=2, U=0.50; when R=4, U=0.25 and so on.  Make sense? 

From this you can figure out how long the heat you create is retained in whatever "vessel" you contain that heat in....to a point.  Now you need to gain an understanding of ACH or Air exchanges. No matter how "tight" your vehicle is, its going to leak air and that has as much effect on heat retention as anything.  What amount of air flows through your vehicle. 

One of the reason PolyIso is liked is because its nearly impenetrable.  Its generally foil or other metallic backed so its stops airflow, as well as moisture. The same can not be said for XPS which is somewhat porous and is self supporting if you will.  Another reason for the PolyIso preference of many working with it, is its actually easier to work with, it cuts cleaner and you can if you have the patience work it around a curve.  However, as has been pointed out, it breaks down with age more so than XPS.  In fact, big untalked about factor is all insulation breaks, and wears down.  If its more than ten years old, its likely not doing the job you once thought anymore.  

Okay, so now we've got our insulation technical factors to help us select the insulation.  We've got our heat load calculations and next we'll want to look at ACH...which I'm not going to give you because its a whole lotta writing and figuring, and it changes with each year your vehicle ages, and your insulation compacts and your weather gaskets do what they do.   And that without mentioning that each modification you make will change that again.  You have to think of the whole vehicle....its a system.  Reality is, and you alluded to moisture if one were to use spay in foam...well, reality, if its done write you shouldn't have any problem because you'll use a moisture barrier, and with the proper ACH in the van any moisture will be moved out before it can create a problem.  Likewise some of the more unique insulation, blown in wool for example takes care of the moisture on its own, and actually uses it for insulating support. 

I can give you a million reasons not to use PolyIso or XPS, each at best is a compromise that will not conform to the vehicle and therefore wastes space and hampers its own efficiency.  BTW: Why do people seem to choose one PolyIso over the other XPS?  Simple Poly is nicer and easier to work with.  Its also less confusing to purchase.  Though not always obvious, XPS comes not only in different thicknesses to give R-Value but also different densities.  The more dense product is a bear to work with.  PolyIso comes in thicknesses, and the thicker the almost easier to work with.  So there is that.  

If you were to seal the hell out of the vehicle, you would find you needed nearly no insulation to maintain a very comfortable living space.  But...that is not the case.  You also have to factor in thermal transfer....a whole other topic to consider in your quest for the ultimate insulation. 

Another issue that make no one insulation best is where are you going to be traveling?  PolyIso's performance in some climates is not real long for this world.  Its will literally turn to dust over a relatively short time.  XPS will not, though it too will suffer.  Fabric insulation like wool or denim don't care if they are in the arctic  or dessert.  On the other hand, oh....wait...ran out of hands. 

Sincerely hope this helps you. 

If you want to further understand some of this, I'd suggest a book, available in most libraries or relatively inexpensive in book stores: Residential Energy:Cost Savings and Comfort for existing Buildings by John Krigger and Chris Dorsi. 

Thanks for reading.  Hope I calmed some of the hostilities. 

 

[AngryVanMan]

1.  You said, "As insulation, new PolyIso is better than XPS (higher R-value). Aged PolyIso is better than XPS, maintaining a higher overall R-value as well. They are very similarly priced. It follows that, as insulation, PolyIso is better."  You seem to limit the definition of "best" to solely highest R-value.  Is that perhaps too limiting, needing to be expanded by including some other factors before totaling to "best", or just the only factor worth really considering in your opinion?

That paragraph is qualified with the first two words "as insuation" - meaning that, since R-value is the performance measure of insulation, the insulation with the best performance is the best insulation.

2.  You said, "PolyIso is more rigid of the two choices, so it could be easier to ham-fist the install of the less forgiving product."  Lost me here.  Your conclusion doesn't seem to match the beginning of the sentence.  I would have finished your sentence with "more forgiving".  What am I missing?

Forgiving is used here in the cast iron vs. steel sense of the word; the ability of a material to yield to physical forces exerted on its structure without sustaining permanent damage.

Although the math probably speaks for itself, maybe someone will run across an authoritative online source saying simply what you said -- the R-value scale is linear.  If not, I'm OK with that.

The mathematical equation of a measurable property is the simplest way to convey this relationship. R-value is a special abstraction of thermal resistance normalized to material thickness. Thermal resistance is a analogue to electrical and hydraulic resistance, and is a steady-state simplified property derived from the heat equation, a parabolic partial differential equation that itself is a product of the first law of thermodynamics and the state equation. The electrical/hydraulic analogies are explained more fully in the Thermal Resistance wiki page if it would be helpful.

Thermal resistance, and by extension R-value, are linear because they are specifically modeled as a linear variable to describe, in the most simplified terms, the heat flow through a surface. Abstractions like this are specifically developed mathematically so we can make common-sense material comparisons using simplified properties. We do the same thing with Ohm's law in electronics, the Hagen-Poiseulle equation in hydraulics, and Hooke's law in mechanical structures. These are called lumped element linear models - they are simplifications of the Calculus involved for the purpose of quick and easy functional design in the respective fields of inquiry.

The Wiki page and its sources give this conclusion, but the writing is technical and the purpose of our R-value and resistance abstractions are not clearly stated in a succint fashion. Linear modelling is the only reason these variables exist.

 

[DannyB1954]

 The cold air, and colder air radiating from the ground is going to reach the outer floor of the van, and then once it sufficiently cools the bottom of the vehicle, it will conduct that cold to the rest of the sheet metal, and then the thermodynamics kicks in 

A law of thermodynamics is heat flows from warm to cold. Not the other way around. The larger the temperature differences, the quicker the heat energy will move. Cold does not radiate. Heat is energy. Cold is a lack of energy. You can not have a lack of something flowing into a supply of something. It is impossible to add cold to anything. You can only move the heat. 

I looked at all the insulation that Home Depot sells. Per inch they are not all that different. What is a bigger factor is how do their other characteristics play in the installation. The best insulator that does not fit well into the space is not as good as the worst insulator that fits perfectly. I personally don't like foam board of any type. If moisture gets behind it for any reason, that moisture will not easily evaporate. I am especially leery of things that give off toxic fumes when they burn. 

I am leaning towards Denum. If something can get wet easy, it can dry easy as well. Under the front mats of all vehicles is a fiber insulation that all manufacturers use to keep engine heat and noise out of the passenger compartment. I bet the engineers know more than any of us. Everybody has spiled something in their vehicle. Did the floor rot out before it dried? Now spill something and cover it in a vapor barrier and see what happens. 

I did Transport Refrigeration for over 30 years. I was a Reefer Mechanic. Carrier Thermo-King, Mitsubishi Daikin etc. Over the road and sea going.