1. If the cup is used for a long time, it is inevitable that there will be bumps and dents, and the damage to the outer shell of the cup may lead to vacuum contact with the interlayer, resulting in the cup being unable to keep warm.
2. You can check if the cup cover is damaged. If it is not damaged, you can check if the sealing gasket has fallen off. If the sealing is not good, air can enter the cup and it will also cause insulation failure.
3. Some businesses, in order to make money and seize the consumer's desire for cheap goods, put sand into the gap between the outer shell and the interlayer. Because there is sand placed in the interlayer, it can have a certain insulation effect. However, over time, sand can cause the inner liner to rust, resulting in poor temperature retention of the cup.