Reflectix vs. aluminized foam board on windows

[ganchan]

Which material is more effective and versatile for insulating windows, Reflectix or foam board with a reflective foil coating on one side?


They both look easy enough to attach, although the foam board has the edge in that it can hold its shape in the frame without any outside aid. Cost of both materials appears comparable.

I do like the idea of painting the non-foil side of foam board panels black. I could face the reflective side outward on hot days to bounce sunlight away from the windows, or I could face the black side outward to absorb incoming thermal energy while the foil side reflects my own body heat back at me on cold days....

 

[DannyB1954]

My vote between the two would be foam board. Reflectix has very little insulation value. It was designed to lay on top of insulation and reflect radiant heat.

 

[LeeRevell]

Reflectix is a thermal barrier.
Foam board (polyiso) is insulation (with or without the foil).
Different items for different purposes.

 

[Vagabound]

Reflectix is a thermal barrier.
Foam board (polyiso) is insulation (with or without the foil).
Different items for different purposes.

Hi Lee,

OK, I'll bite ... if the purpose of insulation is not to keep one temp on one side, and another temp on the other side (= thermal barrier), then what is it for?  

This might be some insulation nuance / terminology that I'm not seeing or not familiar with.

Vagabound

 

[RVTravel]

Some use both for windows, with polyiso sandwiched between reflectix (Reflectix/½"iso/Reflectix)

 

[Optimistic Paranoid]

Heat transfers through one or more of three methods.  Convection, conduction, and radiation.

Reflectix prevents the transfer of heat by radiation, (by reflecting the radiant energy like a mirror) but has no real insulation value - aka "R-value).  It does nothing to prevent convection or conduction transfer.

Plain foam board will have an R-value and will prevent convection and conduction, but cannot reflect radiant heat.  Instead, it will absorb any radiant heat that passes through the glass and will itself necessarily heat up.  It's great inside the walls of conventional buildings because radiant heat isn't really a factor there.

Aluminized foam board copes with all three types of heat transfer and is ideal for use in windows for that reason.

 

[TrainChaser]

Nicely phrased, OP! That was helpful.

Also, the foamboard will help contain heat inside when you need it, and Reflectix won't.

I am trying to figure out how many cats it would take to keep the van warm (w/me in it, too) on a 40F night..... The only info I've seen in the past involved sled dogs and igloos.

 

[ganchan]

Nicely phrased, OP!  That was helpful.

Also, the foamboard will help contain heat inside when you need it, and Reflectix won't.

I am trying to figure out how many cats it would take to keep the van warm (w/me in it, too) on a 40F night.....  The only info I've seen in the past involved sled dogs and igloos.

I'll be inside a 30-degree sleeping bag, with maybe a thick comforter draped over it. I might not be comfortable, but I'll still be alive come the dawn....

Any temp below freezing, and I'll be in a motel room for the night or on my way to a warmer climate. 

Yeah, looks like foil-backed foam is the way to go. This stuff has a R-value of +3.2. Good enough? There's also an R5 version, but it's 3/4 inch.

 

[zuren]

How durable is the foil backed foam? From my limited use and memory, it likes to crumble when abused on the edges. Maybe it was a different product. I would think it would work well if installed and left in place. For someone like me who wants to easily install and remove my insulation panels frequently, I fear the mess it may make.

I just bought a roll of Reflectix myself. While not a perfect solution, it seems to be better than nothing. I'm toying with the idea of adding a panel of 1/4" foam insulation to the Refectix (against the window glass) but that only brings my total R value to 2ish.

 

[SternWake]

I found when one rolls and unrolls / folds reflectix a bunch, it gets shorter and shorter, and one needs to add extensions to the edges of their cut to size panels.

The foam board panels come in EPS and isocynate. The edges of either can get trashed over time.

one option can be covering them with tape, or perhaps some thin strips of Oak or pine and taping over them.

I like the Nashua Flexfix tape for all silver tape duty.

Getting panels tight to the windows makes a big difference. the dead air space thing and all. many window curve inward and there will be some superheated air in the gap that should be contained there.

I disagree with the statements that reflectix has NO insulative value and only works to reflect radiant heat or as a vapor barrier. It is only ~1/4 inch thick, but it is a dead air space. Layer it as thick (and seal the edges) as a foam board panel and I doubt the R values would be much different.

Don't forget about emissivity, the ability of a surface to emit heat. Silver reflects heat, but also emits the least of any color.

The silver of reflectix is much shinier than the dull matte gray finish of foam board panels. Meaning a lower emissivity, meaning less radiant heat from the heated insulation.

 

[TrainChaser]

From the Reflectix company at http://www.reflectixinc.com/basepage.asp?PageIndex=389

"If You Install 2 Layers of a Reflective Insulation, Does the R-value Double?
With multiple layers of product and airspaces between each layer, enhanced performance will be gained. If the product is simply “doubled” (with no air space between the layers), a very minimal benefit is obtained (R-1.1 (per layer) for the Reflective/Double Bubble product)."

I don't think I've ever seen the "Double Bubble" product...

 

[SternWake]

As I type this, my back door windows are facing south in full sun at 2PM

I have an IR thermometer and will hold it tightly to 1 layer of reflectix, 2 layers of reflectix and the curtain( black facing sun and browning facing inward.

1 layer: 96.5f

2 layers: 88.0F

No layers: 113.5f

placing my hand 6 inches from curtain with of the no layers of reflectix feels like it is in direct sun.

Cant really feel much heat in front of single layer, and non in front of dual layers.

The two layers is just the reflextic folded over. There is a minimal airspace between them, not sealed.

This is not true reflectix but dollar store window shades I hold to my back tinted windows with black bungee cords hooked over rope cleats.

 

[Vagabound]

As I type this, my back door windows are facing south in full sun at 2PM

I have an IR thermometer and will hold it tightly to 1 layer of reflectix, 2 layers of reflectix and the curtain( black facing sun and browning facing inward.

...

I love me some experiments!

Vagabound

---------------

"I don't know why you always have to be judging me because I only believe in science."
-- Esqueleto

 

[ArtW]

Nicely phrased, OP! That was helpful.

Also, the foamboard will help contain heat inside when you need it, and Reflectix won't.

I am trying to figure out how many cats it would take to keep the van warm (w/me in it, too) on a 40F night..... The only info I've seen in the past involved sled dogs and igloos.

I've had as many as 8 in bed with me, pretty durn toasty, with decent covers
poor kitties suffered if they tried being foot warmers, though, apparently I object to things on my feet while sleeping, and some of them got airborne now and then

 

[TrainChaser]

Yes, there is a problem when cats insist of being ON TOP of you, instead of just snuggled beside you.

 

[DannyB1954]

An 8 cat night doesn't have the same ring as 3 dog night.

 

[Vagabound]

Yes, there is a problem when cats ...

You could've just stopped there. ;-)

Vagabound

 

[TrainChaser]

Art started it.

 

[Vagabound]

I'm telling Mom!

 

[Almost There]

Mom just heard that...yes, she has eyes in the back of her head and extreme hearing ability!..

Now just quit it with the cat stuff!!

Back to the subject please!!

Or no desert for any of you....