I don't understand the need for that much padding in a potholder. We're not talking molten pig-iron here. LOL
If you use thin stuff like warm and natural, another layer probably would be needed, but regular high loft batting and even low loft, even one layer is sufficient.
I made one of those bowl holders that asks for two layers of batt. I used only one, of polyester, and it works just fine. I've used it multiple times. I've never seen polyester melt. Maybe it would if you left the iron on it long enough to scorch.
My favorite pot holders are just two layers of old Turkish towel. (It was a nice heavy towel.) Never need more than one. I should cover them with some pretty fabric, but I'm too busy using them to take the time.