I use a pellon ultra lightweight fusible. I also bought a bolt at Joann's. I've made 4 t-shirt quilt so far.

I like 911ff its a fusible featherweight. But my LQS carries a Sew Lazy brand that is just awesome!! I do really love it...no pressing cloth needed and interfacing goes so much quicker. The only down side is that it is alot more expensive than the other brands

Well, I don't use any kind of fusible. Because I live so far away from any store that sells fusibles AND because I wanted to start my quilt at night, I ironed FREEZER PAPER on to the back of my t-shirts. Then I cut out my blocks, and then sewed cotton sashing strips to all four sides. Removed the paper and made my quilt top. Works for me.

I prefer Pellon brand but I have used JoAnn's store brand that used to sell for .99 per yard and that worked fine as well.