Hot water bottle
||This article relies largely or entirely upon a single source. (January 2012)|
A hot water bottle (or hottie or Dutch wife) is a container filled with hot water and sealed with a stopper, used to provide warmth, typically whilst in bed, but also for the application of heat to a specific part of the body.
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.
Rubber bottles 
Modern day conventional hot water bottles were invented in 1903 and are manufactured in natural rubber or PVC, to a design patented by the Croatian inventor Eduard Penkala. They are now commonly covered in fabric, sometimes with a novelty design.
By the late 20th century, the use of hot water bottles had markedly declined around most of the world. Not only were homes better heated, but newer items such as electric blankets were competing with hot water bottles as a source of night-time heat. However hot water bottles continue to remain as a popular alternative in Ireland and the United Kingdom, developing countries and rural areas. For example, it is widely used in Chile, where it is called a "guatero". There has been a recent surge in popularity in Japan where it is seen as an ecologically friendly and thrifty way to keep warm.
Some newer products function like the older bottles, but use a polymer gel or wax in a heat pad. The pads can be heated in a microwave oven, and they are marketed as safer than liquid-filled bottles or electrically-heated devices.
While generally used for keeping warm, conventional hot water bottles can be used to some effect for the local application of heat as a medical treatment, for example for pain relief; but here also, newer items such as purpose-designed heating pads are now often used.
There have been problems with premature failure of rubber hot water bottles due to faulty manufacture. The rubber may become brittle if manufacturing is not controlled closely enough. 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.
See also 
- Lewis, Leo (November 29, 2008). "Japan's thrifty find the hot water bottle to survive the chill". The Times.
|Wikimedia Commons has media related to: Hot-water bottles|