Tshirts being fully cotton, would work either way, In my church, we use old sheets as batting for our quilts that go overseas, that I would think if you put tshirts together, they would work just was well. In the old times, people used lightweight fabric as batting for summer quilts. I also think that tshirts being cotton would work as hot pads, if you had enough layers, they would be better than polyester batting, due to the heat and melting. I also think if you use them and insulate it would give the potholder some poof as well as insulation. That is just my opinion of course.