One idea::: At our local fabric store, a clerk suggested I purchase the silver, material that is used in ironing board covers. It is thin and cheaper than insul-brite that is ofter used in potholders and less bulky to sew.
Cut 2 squares of the silver material and one square of the cotton batting ( cotton absorbs the moisture and wont melt, like poly batts) Place the cotton batt between the 2 silver squares (siver side faces out in order to make both sides of your potholders heat resistant. Good luck. copycat