So I cannot thank you guys enough for this conversation. I have only been costuming for about a year and a half and only a short time ago went from just sewing to attempting armors, etc. So I had been fibergalssing over Pep. While that makes for an extremely durable end, it is super messy and takes forever. So only a couple weeks ago I started looking into foam. I got a bunch of that 2mm stuff and was so horribly disappointed with the results. Also, in attempting to seal it, it bent so easily that the sealing just cracked right up. So I just got a few sheets of the 6mm(1/4") from Michaels, the regular paper sized. I did a quick base of a Magneto helmet and love the rigidity. But the sealing is still a no-dice, so I actually experimented with "sealing" with fiberglass resin, sans clothe. absolutely loved the result. But despite reading up on EVA foams and looking at pictures, it still was not terribly clear to me what I really needed to look for. So in comes this thread and I have SUCH a clearer idea of what I need. I was looking at web-sites(because I want to get large sheets for ease of large pieces), but after shipping costs, prices nearly doubled. It is New Years Day, so nowhere is open. But I am now stoked to hop out to Big Lots and Sears and Play It Again Sports to scope out some fatigue mats and yoga mats.
So thank you guys again.