I have made two using a non-woven fusible interfacing.....never had a problem. The hardest part was ironing the interfacing on the shirts....took a long time and was "a hot job"....HeeHee! I did not cut my blocks first, but instead just cut the shirts up the sides and then sewed a 15" square piece of interfacing on the shirt and then did my cutting. Maybe that helped keep it from stretching?????