These three were the most popular ways to keep people warm in winter in 1990 Shanghai. They are all hot water containers.
Glass bottle(Medical waste):
In the first a few years in my life, those were the only heating methods we had. Around 1990, things were not very well made. None of them were very ideal: they burned our skin or they leaked in the bed.
It's hard for people nowadays to imagine putting a super hot glass bottle in the bed. Especially those were medical waste. But at that time, that was the most reasonable choice.
Cloth wrappers were made for all three kinds of warmers. After we had the first little electric heater, we stopped using them. My Mom kept the Tangpozi deep in the closet until 2-3 years ago. When they moved out of the old house, she gave it to some friend.