I bought the special potato bag batting that is 100% cotton and followed all the rules (all cotton everything) and my sister-in-law had one of her bags catch fire - she sent me pics of the bag - it was in the seam line - my husband said maybe there was too much thread buildup? I don't know what really happened - however I had a friend tell me if you leave them too long in the microwave they will catch fire. After that incident I quilt making potato bags and I no longer sell them either.