If the inner container in the kettle is loose, you can open the kettle shell and check whether the fixing screws for fixing the inner container in the kettle are loose. If the screw is loose, you can tighten it. If the fixed bracket inside is deformed, you can try plastic surgery. If not, you can plug a little sponge to fix it.
The structure of thermos bottle is not complicated. There is a double glass bottle liner in the middle. These two layers are evacuated and plated with silver or aluminum. The vacuum state can avoid thermal convection. Glass itself is a poor conductor of heat, and silver-plated glass can reflect the heat energy radiated from the container. On the contrary, if the cold liquid is stored in the bottle, the bottle can prevent the external heat energy from radiating into the bottle.