I just never wanted to put the extra money into insulbrite. the batting I use is not fat and after the hotpad is quilted down it is not fat anyway. Using 2 layers of batting worked just fine for me. I sold over 900 hotpads in 12 years and never had any complaints. I would not use anything fluffy and thick for batting. I have also heard of people who recycle towels in place of batting.
It is all in what you want to use. I made my decisions when I first started making them. everyone has a different view of how they want their hot pad or pot holder made.