The device uses special gel to generate the heat. (babygearhub.net)
Disposable diapers that contain special gels that keep the baby dry actually keeps the baby's waste matter in contact with the baby's bottom longer than it should. (diaperjunction.com)
Change may be on the horizon though as scientists have completed a successful trial on monkeys for a special gel that can be injected into a man's testicles (yea oww, but I bet it's not as bad as childbirth guys!). (naptimenatter.com)