To make a 5-by-5 inch square double-thick potholder, single chain 26, turn as usual and single chain along the back row to the end of the original chain. At the end of the row, single chain two, turn and chain to the end of the row again. Continue making single chains along the back row until the tops of the rows meet in the middle when the pot holder is folded, and sew the edges closed.
Expect the pot holder to curl at the corners while making rows, and turn the crochet as needed to crochet on both sides of the base. Another option is to chain 23 then single chain beginning in the second single chain from the end of the row. Continue to the end of the row, single chain three, and turn.
Begin using a back front double crochet stitch, and chain four at the end of the first row. Continue using the back front double crochet stitch to form 12 rows. At the end every fourth row, chain one single chain before turning. At the end of all other rows, double chain and turn.
Wash and dry the pot holder to tighten the stitches before using it. For best results, use natural fibers, such as wool or cotton yarn, when making pot holders, as other yarns melt.