Funny this subject came up today! I just bought something for this type project this morning at Joann's. It is on sale for 4 days at 50% off. It is called Pellon SF101 Shape Flex, all purpose woven fusible interfacing. "For garments, and adds body and permanent stability when used as a backing for needlework and punch embroidery". It looks like a lightweight fabric with fusible "glue" on the back.
My LQS also sells a package of what looks close to the same thing and they called it Stacy. They use it for backs of their "fabric with wool embellishment" embroidery squares.