Teardrops n Tiny Travel Trailers

I need good insulation, maybe willing to go 4".

Polyiso is the way to go right?

I'm willing to pay shipping or special order from a smaller shop if HD or Lowe's don't stock the good stuff.

I don't have a Menards near me, but this looked ideal, fiberglass faced on both sides, great price too, right?

Johns Manville ValuTherm
https://www.menards.com/main/building-m ... 917954.htm

Hopefully some who has actually built a foamy will chime in, but this is what I think most have used:

Owens Corning® Foamular® Extruded Polystyrene Insulation 2" x 4' x 8' R-10 at Menards https://www.menards.com/main/p-1444450471143.htm

GPW's FoamStream is the only one that I can remember is 4". He'd have to say for sure but I think the primary reason for going that thick was the deal he got on the foam.

The 4" is 20% less insulating, cost 50% more and has no facing.

I know XPS is supposed to be a bit stronger than polyiso, but foamie construction gets most of its strength from the fabric+goop skin.

So a factory bonding of fiberglass skin, I'm thinking will likely more than compensate, make for a finished composite with much greater shear, tensile, and compressive strength.

Yes, Polyiso is weaker than XPS. That is why all the polyiso sheets you will find have a facing of some kind, foil is common. I have no idea how heavy the f'glass on those fiberglass faced sheets are. Just keep in mind that the only real reason for the facing is to keep the polyiso from coming apart while it is being handled.

Polyiso absorbs water more readily than XPS or EPS foam. That's probably not a factor unless you are insulating under a concrete slab for a house.

FYI, polyiso insulates better against high temperatures than it does when it is very cold. The R-value of polyiso actually decreases as the temperature falls. You can google and find specific performance numbers, but the reduced R-value is a reason that polyiso is not recommended for houses in northern climates. On the other hand here in the SW where heat is more of a factor we used polyiso both in out trailer and our home.

That last is interesting, did some reading, but I think the issue is not a major one for my use case.

polyisocyanurate … That seems to be the problem ! Hot wiring gives off toxic fumes ( or fire ) and the stuff we tried (years ago) was brittle . If you crush it it turns to dust , and doesn’t Heal in the Sun like the other foams . We avoid it at all cost !
We used the EPS expanded poly styrene , for it’s more innocuous properties , (plus we got big blocks cheap ) The reason I used 3.5” thickness was it’s not as strong as the XPS ( extruded foam ) , so according to the property … “ Twice as thick is 8 times stronger” … that was the way to go . we did want some structural element to the foam , although it was applied over the wooden frame and then covered with thick canvas.

But don’t believe me … https://en.wikipedia.org/wiki/Polyisocyanurate

John61CT wrote:I need good insulation, maybe willing to go 4".

Polyiso is the way to go right?

I'm willing to pay shipping or special order from a smaller shop if HD or Lowe's don't stock the good stuff.

I don't have a Menards near me, but this looked ideal, fiberglass faced on both sides, great price too, right?

Johns Manville ValuTherm
https://www.menards.com/main/building-m ... 917954.htm

I looked at the Menards page and the facing skin doesn't look like fiberglass. It looks more like hardboard. On the JM website is says "glass fiber reinforced": https://www.jm.com/content/dam/jm/global/en/commercial-roofing/Data%20sheets/Insulation/RS-5174_FlatTaperedValuTherm.pdf. Regardless, I think it would make a good substrate for fiberglass.

Thanks.

I wasn't planning on real fiberglass, more based on PMF foamie

XPS is the way to go. It handles, forms and cuts much better than crumbly polyiso.

Glues and techniques that work with XPS/EPS are well documented here; polyiso, not so much.

Panther pink ("Foamular" brand) or Dow blue ("Styrofoam" brand). I think Menard's used to carry an equivalent XPS that was colored green.

As noted above, just to recap;
EPS = Expanded polystyrene... the little balls pressed and molded together, like foam coffee cups and those cheap coolers that you buy at the convenience stores, usually white.

XPS = Extruded polystyrene... wall board insulation, "folded fan board" insulation, underlay insulation for concrete slabs and foundation walls, usually pink or blue, thinner sizes (below 1 inch thk) may have a clear film reinforcing that should be peeled off before attempting to glue.

polyiso (for short) or polyisocyanurate = more fragile, brittle and crumbly, usually has a reinforcing film, yellow-ish... not good for "traditional" foamie construction techniques.

The thermal performance and cost differences of polyiso do not win out against the workability and handling properties of XPS.

I just bought a sheet of the new Fomular to ship off my Flamingoes , and it’s not the old Pink foam …. This seems even denser … and was a purply’ pink color … kinda’ Cool really … Yet to make anything out of it save a big box . And it doesn’t like E3000 Goop ( tested-failed !!!) melts the foam …