Abstract: A heat pack capable of being heated to at least 55.degree. C. is provided and includes a flexible impervious outer container capable of being sealed to retain a liquid such as water therein and of maintaining its sealed integrity when heated to at least the aforesaid temperature. A porous, non-rigid filing material, which can absorb at least its own weight of the liquid, is located in the container. Advantageously, the pack contains a weight of liquid in the range 250 goods to 1250 goods, which liquid is water or compounds having one or more hydroxyl groups, or a mixture of water and such hydroxyl group compounds. In order to prevent microbial growth within the liquid-filled, sealed container, a predetermined quantity of a preservative at an appropriate concentration is also added to the fill. The filling material is preferably either fibrous or spongy in nature and advantageously may be a textile material or paper which is either recycled or would otherwise be treated as scrap or waste.