definitely us an intefacing. I used tricot and put the stretch in the opposite direction of the stretch on the tee shirts. I like it because it stays very soft. Be sure to apply the interfacing before you cut the tee shirt to keep the edges stable. The one I made had come from various sized designs. I measured the smallest and largest. sketched them on paper to gauge how much of a border i wanted on each, then trimmed them all to the same size. I used a wiggly stripe sashing between the blocks to help me tie in all the different colors from the tee shirts. Other than the interfacing and size difference, it's just like making a cotton quilt. A bit heavier to move around when doing quilting on a domestic machine though. Be sure to have a table or something to support it if you are quilting it yourself.