Craft foam is an inexpensive and easy to use material for making things. It is kind of like a cloth and kind of like a
sponge. ...
Other names for it are
Foam Sheets and Foamies. Typically the sheets are about 2mm thick. But you can get it in a wide variety of sizes and thicknesses.
They are made of ethylene-vinyl acetate copolymer foam, or
EVA, a durable plastic foam that is an alternative to materials such as rubber and vinyl often used because of its ability to remain strong at low temperatures and its resistance to UV rays and cracking.