Hi Sunnyflower. The ice packs have a somewhat thick knit cloth covering. Inside is a removable clay slab that doesn't get so cold that it could freeze the skin. It is just the right amount of cold. If it feels too cold you can put it on over socks or pant legs but that reduces the effectiveness somewhat. They start to warm up or defrost within a few minutes and the slab becomes more pliable. These have really been a life saver for me. They can also be heated in the microwave but I have never tried that. Your warning is appropriate nonetheless. Thanks.