I bought some in the dollar store they were big and different shapes try there ok

Neoprene sounds like what you are looking for and not knowing where you live here in the U.S. have found it at JoAnn's Fabrics. Do a search on line and see if there is any available in your area or even at a marine supplier. Or do like noah said below and buy a can koozie at one of the dollar stores and take it apart for the fabric. I have seen them in different sizes and even with a zipper

Would Fun Foam work? You may be able to get it at Walmart or Michael's.
Hugs Jerri