In winter, heat pack called “Hokkairo” is one of the must-have items. Average temperature of 127F (53C) and lasts for 14 hours. There are 2 types of Hokkairo, one with sticker and one without sticker. One with sticker can be used to put on your cloth to keep it warm. So, if you want to keep your belly warm, you can. Just avoid to stick it to your skin directly. 127F may not hot enough to give you immediate burn but can give you moderate-temperature burn.
Peeling off the sticker. There are 2 stickers, on top and bottom.