<P> 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 the hot - water bottle remains a popular alternative in Australia, Ireland, 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 . </P> <P> 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 . Some newer bottles now use a silicone - based material instead of rubber, which resists very hot water better, and does not deteriorate as much as rubber . Although the stopper size in Ireland and the UK has been largely standard for many decades, the newer bottles (notably those from German manufacturer Fashy) use a wider mouth which is easier to fill (and a larger stopper to fit it). </P> <P> 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 newer items such as purpose - designed heating pads are often used now . </P> <Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (September 2016) (Learn how and when to remove this template message) </Td> </Tr> </Table>

When was the rubber hot water bottle invented