Tang Po Zi (汤婆子) is a brass warmer. The name literally means hot water grandma.
(photo from internet)
When my Mom married my Dad, they both were poor and didn't own much. She moved in with only a few things, and Tangpozi was one of them.
We always poured boiling water in so it could stay warm longer. It was made of brass which conducts heat very well. In order to prevent burning, My Mom made some sort of wrapper with old clothes to wrap it up. But minor burning still oftened happened. I loved Tangpozi, I also was kinda scared of it.
We stopped using it a few years after I was born because it wasn’t safe enough.