I use 100% cotton towels. 2 layers. I attach each individual towel square to each front-back of the potholder. I then sandwich the pieces (4) together, treating it like a mini quilt and pin the heck out of it. Then I quilt it, trim it and bind it. I use the walking foot for the entire process and they've all been coming out great.
I've had so much success using cotton towels as batting that I've never gotten around to using the insul-bright(?) The potholders are very soft and fluffy and do really well at keeping your pinkies from burning.