I ordered the 80x96 and 40x96 slabs of 6" foam. My project had round and curved cushions - much like puzzle pieces. I haven't worked with this foam much and when I have it's been for linear projects. I bought a heat knife to cut the shapes as it would've taken me a week to scissor cut. The heat knife worked well but I probably had it on too high. The material melted and hard, sharp plastic pieces on the edges were the result.
I unpackaged the foam immediately on receipt and it layed flat out for several days. The compression was uneven on the larger slab (80x96) and it didn't bounce back evenly. There were ripples in the center and the edges were angled. It was a lot of labor using this material. It's what was called for for this project and I just want to educate anyone who might not be familiar with working with this material.
If I could've, I would've ordered several of the smaller slabs (40x96). Those seemed to bounce back to normal. Unfortunately, my sizes and shapes exceeded those parameters. I just hope this is helpful to users.