Inverted water leakage test
Fill the cup with hot water (not to the top, leaving a small amount of air), tighten the lid, invert and let it stand for 2 to 5 minutes, and shake it a few times. If there is no water leakage or dripping, it is considered qualified; if water droplets leak, it indicates poor sealing.
Note
The internal pressure of hot water is high, and slight steam emission is normal, not a sign of leakage.
Negative pressure suction test
Pour in boiling water, tighten the lid, and let it cool for a few minutes. If there is a noticeable suction when opening the lid and a “poof” sound is heard, it indicates good sealing; if the lid can be easily unscrewed without suction, it is likely that the seal is poor.
