I purchased this hot water bottle for one reason only: provide non electric heat to castor oil pack. When I first started using this pack it seemed to not get as hot as I would have liked, but after a few uses, it heated hot enough in 10 to 15 minutes and stayed hot long enough for a treatment. Keep in mind that it does cool down towards the end of the treatment, just as a regular red rubber hot water bottle. The belt secures the pack right over the liver area and stays put with the Velcro closure. Yes, there is a hard heating element in the middle of the pack, but once in place you are not aware of if unless you are lying right on it, which I'm not. As for instant heat, who can't wait 10 to 15 minutes for hot water? Please, stay away from the microwave! Even though this pack is heated electrically, once the pack is heated there is no electricity running through the unit which meets my criteria of "no electric heat over the pack!" I highly recommend this portable hot water bottle.