Hmm. That doesn't sound like the stuff we use. Linacoustic RC isn't yellow and doesn't have a foil backing. Double check with your supplier and ask him if "Linacoustic Permacoat Duct Liner" rings a bell. He might recognize it by that. It typically comes in 48" x 100 ft rolls, is 1" thick, is black, soft like fiberglass, and one side has a black coating on it to make it a little stiffer, but still flexible.