https://www.mcmaster.com/86375k64/
Also known as Poron:
https://rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes/poron-evextend
Foam compresses 25% at 11psi.
If you buy 1/4" foam, then plan for 3/16" between your cells when you design your busbars and your box, and...