I don't think you'll find high density foam at builders. Trimmers are people that re-upholster furniture and car seats etc. You should also be able to get it from a mattress place... the ones that manufacture mattresses not a normal retailer.

Picture of what high density foam looks like:



Most common seen application for high density foam:



Hope this helps.

Try Mattress factory, any place that sales beds, also upholsterer will have or point you in the right direction.

I have been looking at those Exo Terra Foam backdrops that they use in the water dragons design or any thing that lives in an water environment.

I have always been told to never have sponge in a spider enclosure as a sponge can breed bacteria.
there are a couple things that come to mind thinking about having foam in a spider cage.
1^ST. our spider will tear the sponge apart like a rag doll.
2^ND. The crickets will eat it and make hole in it.
3^RD. As much as your spider can climb, one would think he will get stuck on the foam, not dangerous but I think it will be a bit awkward for the spider to work and get hooked.(just me)
4^TH. And then foam will shock up the moisture add that with the substrate add that with bolus and crickets running around and the spider maybe doing he's busy on the foam you will end up with a perfect breeding ground for bacteria.

at the end of the day it might all sound to be a bit gayish or pampering far to much to the spider but I was told buy more than one person don't put sponge into your enclosure.

@ Cascade - The high density foam absorbing moisture (causing molt problems makes sense but if its covered properly with the marine silicone before adding the rest of the backing, will it still pose a problem? Especially if its used in enclosures that houses larger T's that don't get misted any more, but just has a water bowl?

If you do it that way, then I'm on the fence about this one?! :whistle:

I think if you do it properly and then you give it a trial run in very moist enclosure and then in a very dry enclosure and see what happens.

How much silicone will you end up using to cover the design?.
Once the silicone is on and dry will it stay stack to the foam? (I'm sure it will stick)