Hot water bottle

Prior to the invention of rubber that could withstand sufficient heat, these early hot-water bottles were made of a variety of materials, such as zinc, copper,[1] brass,[2] glass,[3] earthenware[4][3][5] or wood.

To prevent burning, the metal hot water flasks were wrapped in a soft cloth bag.

Some newer products function like the older bottles, but use a polymer gel or wax in a heating pad.

Natural rubber filled with calcium carbonate is the most common material used, but is susceptible to oxidation and polymer degradation at the high temperatures used in shaping the product.

Even though the brittle cracks may not be visible externally, the bottle can fracture suddenly after filling with hot water, and can scald the user—sometimes requiring hospitalization for severe burn cases.

Antique metal hot-water bottle from 1925
English Stoneware bed warmer and stopper
Two modern hot-water bottles shown with their stoppers
An American pottery hot water bottle
Japanese style plastic hot-water bottle, known locally as a yutanpo , with its cloth protective bag on the right.
Pain relief using a hot water bottle
Pain relief using a hot water bottle