Harm to health. Some thermos cups can hold coffee, while others can't. For example, stainless steel thermos cups can't hold coffee. Because there is a substance in coffee called tannic acid, tannic acid will react in stainless steel thermos cups, causing damage to the thermos cups, and may also have chemical effects, thus endangering health.
Cleaning is difficult. The color of coffee is very dark. If the thermos cup soaked in coffee is not cleaned in time, it may cause pigment residue and it is difficult to clean it. And now there are many shapes of thermos cups, and some strange shapes are even more difficult to clean.
Coffee is brewed in a thermos cup, and the coffee will remain heated all the time. It's best to drink it right away. If you can't finish it at once, you should finish it in four hours.
The thermos cup can be filled with hot water in winter and ice water in summer, which also has the function of heat preservation. However, it is best not to put tea, coffee, soy milk and other foods in the thermos cup, which is easy to produce chemical reactions and difficult to clean.