The hot water bottle made of rubber (or similar material) that we use now was invented by Croatian engineer Eduard Penkala (1871–1922). He holds more than 80 patents for inventions, including the "mechanical pencil" ( The prototype of today's mechanical pencil), a pen using solid ink (the prototype of today's ballpoint pen), a braking system for rail vehicles, an anode battery, etc.
Before the invention of this soft hot water bottle, people used containers made of metal, glass, ceramics, wood, etc. to hold hot water and put them on the bed for warmth.