What are the precautions for buying thermos bottles?

What should I pay attention to when buying thermos? 1. See if the gas tail at the bottom of the bottle is complete. If the gas tail is broken or knocked off, it is defective, because the bottle liner is two layers of glass, and there is no air in the middle after pumping. The gas tail is damaged, indicating that air has entered and has no heat preservation effect. 2. Tap the glass on the bottle liner with your fingers. If the sound is crisp, it is a good bottle liner without cracks. 3. Check whether the silver plating (aluminum) is uniform, because silver plating avoids heat radiation and heat loss. 4, with a water bottle stopper, first look at whether the thermos bottle is round, and then plug the bottle stopper and shake it tightly to prevent water leakage. People often choose hot water bottles by listening to the sound, which is unscientific. If the outer glass of the bottle is broken, the inner glass of the bottle will also make a "buzzing" sound, which is the sound made by the convection of air in the bottle. As for the price, there are many reasons. The biggest difference lies in the bottle cap rather than the bottle liner. As long as you choose according to the above method, you will be a good water bottle. You can choose the level according to your hobbies and economic ability.