I used Pellon SF101 when I made mine. I bought a bolt of it in store at Joann's with a 50% off coupon because I use it in making bags and such. It is on sale online only right now.
http://www.joann.com/pellon-sf101-sh...+sf101&start=4
I got a package of June Tailor T Shirt Quilt interfacing once in a grab bag. It looks identical to the Pellon SF101 and was only 3 yards and the price tag on it was $19.99!