1. Listening method.
Attaching the empty bottle to the ear, the greater the better echo!
This is a way to check whether the water bottle is broken. Those voices are formed by the flow of air echo, the greater the better echo!
2. Hot water speed test.
Introducing a half bottle hot water into an empty bottle and close the lid. After about three minutes, try holding the thermos with both hands. If you feel hot, poor insulation performance; if you do not feel hot, indicating good insulation properties.
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