I use a light weight Pelon interfacing for tee shirt quilts. Always remember to cut the tee shirts larger than the finished block size before you add teh stabilizer. I lay the tee shirts face down on a teflon pressing sheet and the fuse the interfacing to the wrong side of the tee shirt. Then and only then, cut the tee shirts to the size blockes you want to use. Stabilizing tee shirts is a must in my book. They stretch when you try to quilt them if you don't.