GPS foam

[Markusbc]

Hi everyone,
Has anyone tried gps foam insulation that is foil backed to insulate the ceiling? Same r value as XPS, I know the permeability is lower on XP’s which is 1.5 vs gps which is 5.0 but with a foil backing it actually goes down to 0.5.
It’s less then half the price then XPs foam. It won’t work for floors because the lack of compression strength but for the ceiling, it should work.

Has anyone used it? Am I missing something why it shouldn’t be used?

 

[dzl_]

Hi everyone,
Has anyone tried gps foam insulation that is foil backed to insulate the ceiling? Same r value as XPS, I know the permeability is lower on XP’s which is .5 vs gps which is 5.0 but with a foil backing it actually goes down to 0.5.
It’s less then half the price then XPs foam. It won’t work for floors because the lack of compression strength but for the ceiling, it should work.

Has anyone used it? Am I missing something why it shouldn’t be used?

Have never heard of GPS foam, a quick google turns up a few results but not a ton, where have you seen it sold?

 

[Markusbc]

At Home Depot

Comes in 4x8 sheets. 1 1/6 thick or 2 1/8 thickness.
Foil covered on both sides. No off gassing and no loss of r- value over time apparently.

 

[dzl_]

After a bit more research, it looks like GPS is a sub-type of EPS



This discussion may interest you

 

[Markusbc]

So it looks like eps stores less moisture then XPs due to a closer cell structure. Yes it is more permeable. Wouldn’t that help with avoiding trapping air against the metal skin.

The down side of eps seems the lower r rating compared to eps and poly... which gps seems to take care of.

I am thinking I might go for gps. Just not sure if I use Vapour barrier over it but then it would allow to trap moisture again. Defeats the purpose.
Any thoughts?

 

[dzl_]

So it looks like eps stores less moisture then XPs due to a closer cell structure. Yes it is more permeable. Wouldn’t that help with avoiding trapping air against the metal skin.

The down side of eps seems the lower r rating compared to eps and poly... which gps seems to take care of.

I am thinking I might go for gps. Just not sure if I use Vapour barrier over it but then it would allow to trap moisture again. Defeats the purpose.
Any thoughts?

I was under the impression that people generally regarded XPS as the better options with regards to moisture. But I may have misunderstood, or may have misunderstood a piece of the context for that preference.

 

[Markusbc]

Yes I also thought so. But from what I have read XP’s will absorb moisture over time and won’t release it. GPS apparently absorbs moisture as well but will dry out again fast. So it might avoid trapping humidity between the foam and the metal skin of the bus.

Also one thing i find appealing g is no blowing agents off gassing compared to XPs and no revalue loss over time. Compared to polyc.. foam The r value of gps apparently Increases the colder it gets outside.

 

[musigenesis]

The R-value of GPS does increase (slightly) with decreasing temperature, but that's normal not just for most types of insulation but also for non-metallic materials in general. Polyiso is the exception to this, with an R-value that increases (slightly) with increasing temperatures (at least within the temperature range that humans inhabit).

The permeability of GPS appears to be intermediate between XPS and EPS; none of these have a low enough permeability to be considered a proper vapor barrier, which is something spray foam achieves. If you're not completely blocking condensation from inside from making its way through the foam to the steel skin, do you want to block it a little or a lot? I dunno, but the difference between XPS and GPS in this case is probably pretty small.

GPS seems like a perfectly viable option for insulation, but not really superior to XPS (unless it's significantly cheaper). I would use it for sure if I found some on Craigslist - in fact I have seen it there before but I didn't know what it was. It looks like the stuff foam sticks for pools are made out of, not exactly promising.

 

[Markusbc]

Foam

Not arguing it’s superior, I was just surprised that I haven’t heard of it before. Up here in bc Canada the prices are, $44 for 2x8 foot for 2 inch xps and $35 for 4x8 foot 2 1/8 gps. So it’s significantly cheaper.

My post is to open up a conversation of the viability of this type of insulation.

 

[Markusbc]

The R-value of GPS does increase (slightly) with decreasing temperature, but that's normal not just for most types of insulation but also for non-metallic materials in general. Polyiso is the exception to this, with an R-value that increases (slightly) with increasing temperatures (at least within the temperature range that humans inhabit).

The permeability of GPS appears to be intermediate between XPS and EPS; none of these have a low enough permeability to be considered a proper vapor barrier, which is something spray foam achieves. If you're not completely blocking condensation from inside from making its way through the foam to the steel skin, do you want to block it a little or a lot? I dunno, but the difference between XPS and GPS in this case is probably pretty small.

GPS seems like a perfectly viable option for insulation, but not really superior to XPS (unless it's significantly cheaper). I would use it for sure if I found some on Craigslist - in fact I have seen it there before but I didn't know what it was. It looks like the stuff foam sticks for pools are made out of, not exactly promising.

It looks more like dark grey eps foam.

 

[musigenesis]

Not arguing it’s superior, I was just surprised that I haven’t heard of it before. Up here in bc Canada the prices are, $44 for 2x8 foot for 2 inch xps and $35 for 4x8 foot 2 1/8 gps. So it’s significantly cheaper.

My post is to open up a conversation of the viability of this type of insulation.

I hope I didn't seem like I was criticizing. I was just trying to add some information.

 

[Markusbc]

Not at all.

Any information is good to have.the more info the better.

 

[Native-SKO]

After a bit more research, it looks like GPS is a sub-type of EPS

This discussion may interest you

This thread and the link above (and others that stem from it) are giving me more to think about in designing the walls, ceiling and floor insulation.