1. Look at the tail of the bottom of the bottle to see if it is complete. If the tail is broken or knocked out, it is a disabled product. Because the bottle liner is two layers of glass, there is no air in the middle, the tail damage indicates that the air has entered, no heat preservation effect.
2. Gently tap on the glass of the bottle with your finger. If the sound is crisp, it is a good bottle without cracks.
3. Check that the silver plating is uniform because the silver plating avoids heat radiation and prevents heat loss.
4. Look at the round of the thermos bottle and check whether the cork is tight or leaking.
It is unscientific to choose a thermos by listening to sounds. A bottle of glass with a broken outer layer of glass, the inner layer of glass gallbladder will also make a "beep" sound, which is the sound of the air inside the bladder during convection.