As far as the batting - heat resistant would be equal to Insulbrite. I have read on this board tho to also put a layer of regular cotton batting for added comfort against the heat. If you have no access to Insulbrite, you could double or triple regular cotton batting.
Do not use polyester batting as it does not resist heat and may melt. If it melts onto skin, it could give second or third degree burns.
If no batting is used, I would be very wary of using it with anything hot. The heat could come through the cotton fabric and burn your hand.
I like how big she makes them. Most hotpads are too small for most jobs.
Love the idea of coasters.