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10-18-2020, 10:56 PM
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#1
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Mini-Skoolie
Join Date: Jun 2020
Location: British Columbia
Posts: 59
Year: 2001
Coachwork: Corbeil
Chassis: International 3800
Engine: Dt466e, Alison 2000 transmission
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GPS foam
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?
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10-18-2020, 11:17 PM
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#2
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Bus Nut
Join Date: Jul 2019
Location: California, Bay Area
Posts: 896
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Quote:
Originally Posted by 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 .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?
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Have never heard of GPS foam, a quick google turns up a few results but not a ton, where have you seen it sold?
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10-18-2020, 11:19 PM
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#3
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Mini-Skoolie
Join Date: Jun 2020
Location: British Columbia
Posts: 59
Year: 2001
Coachwork: Corbeil
Chassis: International 3800
Engine: Dt466e, Alison 2000 transmission
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GPS foam
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.
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10-19-2020, 01:49 AM
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#4
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Bus Nut
Join Date: Jul 2019
Location: California, Bay Area
Posts: 896
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After a bit more research, it looks like GPS is a sub-type of EPS
This discussion may interest you
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10-19-2020, 08:50 AM
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#5
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Mini-Skoolie
Join Date: Jun 2020
Location: British Columbia
Posts: 59
Year: 2001
Coachwork: Corbeil
Chassis: International 3800
Engine: Dt466e, Alison 2000 transmission
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GPS foam
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?
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10-19-2020, 02:29 PM
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#6
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Bus Nut
Join Date: Jul 2019
Location: California, Bay Area
Posts: 896
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Quote:
Originally Posted by 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?
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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.
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10-19-2020, 02:47 PM
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#7
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Mini-Skoolie
Join Date: Jun 2020
Location: British Columbia
Posts: 59
Year: 2001
Coachwork: Corbeil
Chassis: International 3800
Engine: Dt466e, Alison 2000 transmission
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GPS foam
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.
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10-19-2020, 09:07 PM
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#8
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Bus Geek
Join Date: Jan 2019
Location: Philadelphia
Posts: 7,000
Year: 2003
Coachwork: International
Chassis: CE 300
Engine: DT466e
Rated Cap: 65C-43A
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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.
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10-19-2020, 09:14 PM
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#9
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Mini-Skoolie
Join Date: Jun 2020
Location: British Columbia
Posts: 59
Year: 2001
Coachwork: Corbeil
Chassis: International 3800
Engine: Dt466e, Alison 2000 transmission
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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.
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10-19-2020, 09:16 PM
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#10
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Mini-Skoolie
Join Date: Jun 2020
Location: British Columbia
Posts: 59
Year: 2001
Coachwork: Corbeil
Chassis: International 3800
Engine: Dt466e, Alison 2000 transmission
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Quote:
Originally Posted by 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.
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It looks more like dark grey eps foam.
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10-19-2020, 09:28 PM
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#11
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Bus Geek
Join Date: Jan 2019
Location: Philadelphia
Posts: 7,000
Year: 2003
Coachwork: International
Chassis: CE 300
Engine: DT466e
Rated Cap: 65C-43A
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Quote:
Originally Posted by Markusbc
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.
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I hope I didn't seem like I was criticizing. I was just trying to add some information.
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10-20-2020, 12:05 AM
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#12
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Mini-Skoolie
Join Date: Jun 2020
Location: British Columbia
Posts: 59
Year: 2001
Coachwork: Corbeil
Chassis: International 3800
Engine: Dt466e, Alison 2000 transmission
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Not at all.
Any information is good to have.the more info the better.
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10-20-2020, 12:33 AM
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#13
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Bus Geek
Join Date: Sep 2015
Posts: 3,856
Year: 2002
Coachwork: Thomas Built Bus
Chassis: Freightliner FS65
Engine: Caterpillar 3126E Diesel
Rated Cap: 71 Passenger- 30,000 lbs.
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Quote:
Originally Posted by dzl_
After a bit more research, it looks like GPS is a sub-type of EPS
This discussion may interest you
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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.
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