My father was a chemist. Not in the UK sense of the word, which would be a pharmacist in the US. He was the 'mad scientist' kind of chemistry major chemist. Some of that must have rubbed off onto me as I was growing up.
If you use EZ Mount cushion for mounting rubber stamps, you are repeatedly warned not to use acetate to store the stamps. The acetate and the EZ Mount have a bad reaction over time and the EZ Mount will glue itself to the acetate and become ruined.
I use Avery sheet protectors to store my unmounted rubber stamps when I use Aileen's TIOAO and I didn't know if they were acetate or not. So I went to the Avery website and checked. They are polypropylene which, to the best of my knowledge, is not the same thing as acetate. My EZ Mount foam should be safe. I can use the same system for all of my unmounted rubber stamps.
If given a choice, I'd use TIOAO for all of my unmounted rubber. I use a pad under my paper when I stamp, so I don't need a cushion and without the EZ Mount, the stamps are a lot thinner and I can store more in the same space.