Leave it to you to dig deep my friend!

I'm still a little nervous about the foam characteristics of the currently used rings over the long term. I've been buying speaker surrounds to replace deterioriating surrounds for years as a regular part of my business. While the manufacturers of the parts that I buy from insist that the current formula of polyether-based products won't decompose like the previously used polyester-based foam products did, I won't know for sure until time passage proves them right.

FWIW, if I was stamping the rings for airtights, I'd be using Santoprene. It is a synthetic form of butyl rubber, available in a wide variety of stiffnesses, would be excellent for cushioning the edges of your tiny treasures within an airtight holder. This material is also used to make speaker surrounds, has been so (just guessing here) for about ten years. I have seen the material crack, but I've never seen it decompose, much less decompose into a substance that bonds with other materials in the process, like I have seen polyester-based foams do.

Happy New Year! ...gonna be in Vegas for da bowl? I am!

Bob