Imagine a personal heating system that works indoors as well as outdoors, can be taken anywhere, requires little energy, and is independent of any infrastructure. It exists – and is hundreds of years old.
A hot water bottle is a sealable container filled with hot water, often enclosed in a textile cover, which is directly placed against a part of the body for thermal comfort. The hot water bottle is still a common household item in some places – such as the UK and Japan – but it is largely forgotten or disregarded in most of the industrialised world. If people know of it, they usually associate it with pain relief rather than thermal comfort, or they consider its use an outdated practice for the poor and the elderly.
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Kris De Decker

Imagine my surprise to discover that not only are hot water bottles confined almost-entirely to the UK and Japan (more-strictly, I suppose the article should say “the British Isles”; friends in Ireland tell me that they’re popular there too), but that they’re so distinctly confined to these isles that English speakers elsewhere in the world need this article to explain to them what a hot water bottle is and why they’d want one!
I’m a fan of hot water bottles; I’ll sometimes take one – or even two, during a cold snap – to bed. But reading this article feels like reading a guide for aliens living on Earth: explaining everyday things as if you’d never come across them before.