I have made two tshirt quilts and used Pellon 911FF (seems to be the lightest I can find around here) on the backs of the tshirts. I cut the fronts and backs apart equally leaving each as large as possible. I then cut the Pellon larger then the blocks I want (but not quite as wide a the tshirt). Smooth the tshirt face down on the ironing surface and center the Pellon on top (fusible side down!! lol). Then I dampen a larger plain tshirt backing wringing out as much as possible and lay it on top to fully cover the Pellon. Press with a dry iron on cotton setting 10 seconds in each spot starting at one corner and overlapping. By making them oversize, you can then center the design better when you cut with the design up and it also protects your ironing surface from the fusible. Both turned out great and the recipients loved them.