That is indeed the best piece of advice I've read here in a while, especially because Portugal is probably the largest producer of cork and derivates in the world!
We use it a lot from pin up boards, to shoe cushioning, to thermal insulation on walls and ceilings and as soud insulation in studios, as flotation aid in boats, as GRP core material and, of course, to seal wine bottles
Here in Portugal it's a lot cheaper than any kind of synthetic foam and, most important, it is an eco friendly product. It is exctracted from the tree (sobreiro) without damaging it...
Go for for cork! At least you'll be improoving our export rate