Containers for warmth in bed were in use as early as the 16th century. The earliest versions contained hot coals from the dying embers of the fire, and these bed warmers were used to warm the bed before getting into it.
Containers using hot water were soon also used, with the advantage that they could remain in the bed with the sleeper. 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, glass, earthenware or wood. To prevent burning, the metal hot water flasks were wrapped in a soft cloth bag.
Hot water bottles are meant to contain very hot fluids and also supposed to be in contact with human skin. This is therefore of utmost importance to ensure, mainly through standards and regulations, that the closing and welding is stable enough to prevent burns, but also to make sure that the bottle’s chemical components are not dangerous for human health. More generally, it is crucial to certify and assure that hot water bottles, whether manufactured, sold or imported are safe.
For instance, the United Kingdom defined British Standards for hot water bottles to regulate their manufacture and sale as well as to ensure their compliance with allsafety standards. The British Standards BS 1970 and BS 1970:2012 (updated version) define, for instance, the bottles’ filling characteristics, safety instructions, allowed materials and components as well as testing methods such as tensile tests for PVC bottles.
Most regulations applied to a country are generally harmonized in order to be applied and applicable in a larger area, such as a trade zone.