I used double thick all cotton fabric inside my pot holders and it worked perfectly. I use mine daily and they keep the heat out just fine. What I did to test first: I made a pocket of fabric, put on layer in.. tested..too warm (put cookie sheet in oven to get hot).. did one layer cotton puffy fill in.. almost good enough. did one layger cotton puffy filling with one layer of thin cotton quilt batting and that was plenty insulated enough. Two layers of the puffy filling is too hard to get in the machine for me. Three layers of the thin cotton batting also worked. My daughter made over 2 dozen pot holders for gifts this year and they are used and well loved. (her first projects learning how to use a sewing machine).