ForumsDIY ← BOM question

Just discovered the soundplane, looking forward to trying the DIY version. I have a question about the BOM. Specifically the dielectric:
12" by 12" by 1/16" thick Super-Resilient Silicone Foam Rubber

For that item at McMaster Carr there seems to be a firmness option of either firm or extra-firm. Which is the intended firmness for the soundplane?

After testing some 20 different elastomers, I am currently using a natural gum rubber foam that is even better. It's "Quick-Recovery Natural Gum Foam" in the McMaster catalog. I would try soft or extra-soft. I would also try 1/8" thick.

I'll see about revising the DIY info when I have time, please stay in touch and let me know about your project!

I'll also add what I tell everyone, I recommend you try a 1x1 or 2x2 version first, to make some mistakes and discover interesting things before wiring up a bigger device.

It looks like Quick-Recovery Natural Gum Foam isn’t available anymore either. If I search for that on the McMaster page, it shows Resilient Polyurethane Foam Sheets instead. The thicknesses also differ. Do you have any suggestions?

It's the same as natural latex rubber foam. I'm sure there are a ton of suppliers you can find online.