A hot-water bottle is a bottle filled with hot water and sealed with a stopper, used to provide warmth, typically while in bed, but also for the application of heat to a specific part of the body.
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
Slavoljub Eduard Penkala was a Croatian engineer and inventor of Dutch-Polish descent.
Slavoljub Penkala in 1920