I am one of the few on this board that do not use fusible interfacing at all when making T-shirt quilts. I only use fusible interfacing when the T-shirt fabric itself is very thin or when the shirt is mesh (athletic jerseys). I create T-shirts quilts where the blocks are different sizes depending on the design on the T-shirt itself. The blocks are all in increments of 4 inches (plus seam allowance) - from 4 in. x 4 in. up to 16 in. x 16 in. Some blocks are rectangles - ie. 4 x 8, 12 x 8, etc. Since I know they are all in these increments I know that they should fit together (a 4 in. square block sewed to an 8 in square block will sew to a 12 in square block. Therefore if there is any stretch (usually minor), I know to just ease it in.