Bug checking cloth

I once attended a hands on class by rabbi Meyer Safdieh demonstrating how to properly check for bugs. He gave us the opportunity to purchase a cloth and light/magnifying glass to use these skills at home. I recently misplaced my cloth, and don’t know the correct one to buy. Where can I get a replacement? It’s obviously not a cheesecloth, because I’ve tried that.

You can purchase them from the JSOR office.