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[quote="$1"]
Agreed - twisting, etc, aren't the problem, but delams are. While it might cure some pressure dings, still, I'd try for a cooler climate.
doc...
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Makes me wonder - wouldn't a vent in a poly board be a good thing?
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Ahmmm - reasonably dense polyurethane foam isn't that bad, as the wee cells of gas tend to be small and not interconnecting the way many styrene foams are. So, you won't get that much expansion, nor will you get the pressure buildup of the board as a whole looking for a weak spot in the glassing. The expansion is (mostly) in the outer skin. Lets not forget that polyurethane foam is a pretty good insulator, so temps will take a while to equalise.
On the other hand, some styrene foams are so open that water will almost pour through 'em. With those, you have what's effectively a hollow board and venting them makes a lot of sense.
The thing you do want to consider is the temperature range you're subjecting things to, like your board. And that in turn takes us to the Ideal Gas Laws: PV=nRT. Or, Pressure x Volume =number of gas molecules x a constant R x Temperature in absolute degrees, like degrees Kelvin. In the case of the gas in your board, the number of molecules is constant, as is the volume.
Playing with the numbers, and using real degrees, lets say we take a board from freezing (273 degrees Kelvin) to that hot attic ( call it 122 F, 45 C or 318 K) - your gas in your foam want to expand by 318/273 or around 17%.
Add in air pressure changes external to the board and what have you, it's not unbelievable to double that, to around a third. Add to that that while polyester resin is a thermosetting plastic, it does soften a little at elevated temps and you can have some real problems.
Oh, and....ever leave your board out in the sun, say on top of the car or in the bed of an open pickup? 120F isn't the number then, especially if you went nuts with the tribal ( black or other dark colored) graphics. Those get really hot, you can just watch 'em bubble up if you're patient. If you were to touch one of those oh-so-cool black squiggles, you'd find it's not cool at all, more like hot enough to blister your skin.
Call it 80C, not quite boiling. 353 K, resin gets quite soft too. and you're in for a definite delam repair.
The moral of the story? Heat isn't kind to plastic. So, be kind to it, make it last.
doc...