You can use the more expensive ones (wrap and zap) that are marketed specifically to use in microwave or use regular cotton batting that does not have scrim. We have been making and selling the soup cozy holders for years and have never had a problem. We do include a tag that states they are for reheating food and should not be used for more than 3 minutes. We have sold hundreds of sets and not had one person complain to us. Just be sure your fabric, batting AND thread are all 100% cotton.