I use Insul-Brite plus a layer of cotton batting. I had read an article on making pot holders, recommending using both, as the cotton batting would help the Insul-Brite do a better job. I've been making them that way for a long time and I recommend it.

I make potholders out of test blocks. As far as what goes inside, I use old dish towels or mattress pads. Anything that is 100% cotton. It just depends on the thickness of the filler how many layers I use. I find that most burns are from too small size and/or the potholder getting wet. I never make mine smaller than a 9 inch block. Old cloth diapers work real well too. But then I buy cloth diapers for every day dish towels when I can find them. If you are a thrift store shopper old linen table cloths are great for dishtowels and filling for potholders. I even have used a couple for quilt backs.

I just wanted to say thank you for this thread. I noticed a few weeks back that my oven mitt was wearing thin and getting really hot. I downloaded a pattern but didn't get any further because of batting concerns and lack of fabric budget. I also was thinking that I'd like to make a kitchen set for my friends wedding at the end of the month if I can find he right fabric (crows anyone?). So I'm eagerly watching and following the debate.

Old cotton mattress pads work fine. They are heavy and give lot of insulation. But they are hard to come by. The newer mattress pads made with polyester do not insulate very well.

I love to make my pot holders 10x10 in, my hubby has large hands. I use the insul bright also and a layer of cotton bat. DottieBug

I cheated. Years ago, there was a sale on nice little potholders with insulbrite silver on each side of the outside and some inexpensive binding. I think they were going for about fifty cents a piece. I bought a 12 inch stack of them and just covered 2 in my favorite quilting fabric and binding. Those two have lasted over 20 years (I can't kill them!) and they've never failed me with regards to protection from heat. I suppose the remainder will be found in my stash after I pass on. I should leave instructions for the finder to do what I did and then have her will the rest to whomever finds her stash!

I use 3 layers of Warm & Natural batting in my potholders.

If they are going to fed definitely have hot pots on then insul bright or I have used thermal curtain lining. Sorry didn't know about the I insult bite at the time. The thermal lining is also very good for quilt as you go or any project where you need to iron the cotton and want to put things on. It is usually cheaper.
Excuse the spelling my iPad insists it is right and won't let me change it.