Jim,
Barry's die would have deteriorated with or without the foam. Here's Jeffrey's post, regarding the chemical content of dice. It would be a good idea to call Tiny Treasures and see what their foam is made of.

http://www.thechipboard.com/cgi-bin/tcb/tcb.pl?read=310233

I never can remember that stuff, so in "layman's terms"... dice collectors should sniff their dice every now and then ! When they deteriorate, like Barry's did, they smell like vinegar. If you think it smells like vinegar, but aren't sure, put it in a small jar with a lid. After a few days, take the lid off and smell...you'll know immediately! Once this starts, there's no way to stop it/preserve the dice (as far as I know). They will shrink, and the spots will "warp" and often will pop off....it's not pretty!

Another sign of this is if the spots don't feel flush with the die. The plastic has begun to shrink, and is compressing the spots.

Another thing that will happen to dice is crystallization. That's dice made of cellulose nitrate. Again, those dice should be isolated because, once they start to deteriorate, they will speed up the deterioration of dice that are near them. Some dice will only crystallize a tiny bit in the corners, others will totally crystallize to the point that they could totally crumble if you pick them up. If they're crystallizing badly, they can be partially protected by applying a coat or two of clear nail laquer. (NOTE: don't coat dice that smell like vinegar...they'll just become sticky! )

In addition to those two problems, dice that are stored in foam, long term, can pick up an imprint of the foam! Read Jeffrey's post on that one...I know it happens, he sounds like he understands why!

This is probably more than you ever wanted to know about the pitfalls of collecting the little plastic cubes...