You absolutely do have to stabilize the T-shirts. They are cotton knit, not a weave, and anything knit is very fluid. I know there is a stabilizer which is often recommended and which several members of my quilting group say is really hard to work with, and I forget what it is called (Is is "woven"? and you are supposed to place the weave cross ways to the way the knit stretches the most? That's what I think I remember, lol). But I do remember that what they prefer to use is the thinnest one JoAnn's has---It's only about 99 cents a yard and doesn't stretch. Fuse to the backside of the T-shirts before cutting out the squares.