First, in the cold winter, the thermos cup is one of the indispensable items in our daily life. So, why can the thermos cup keep warm?Next, we will discuss this problem from three aspects: the material, structure and insulation principle of the thermos cup.
1. Material. 
Generally, thermos mugs are mainly made of materials such as stainless steel, glass, ceramic, etc. These materials all have excellent thermal insulation properties and are able to maintain the temperature of hot water in cold weather. Among them, stainless steel is one of the most common materials for making thermos cups, because it has good corrosion resistance and strength, and at the same time has good thermal insulation performance. 、
2. Structure. 
The thermos cup is usually constructed of two or three layers, and the middle layer is filled with thermal insulation materials, such as asbestos, ceramics, etc. These materials are able to effectively block the heat transfer between the inner and outer layers, thus maintaining the temperature of the hot water in the cup. In addition, the walls of thermos cups are also usually thick, which helps to reduce heat loss.
3. Thermal insulation principle.
Thermos cups keep warm by blocking the transfer of heat. Specifically, when hot water is loaded into the thermos cup, the heat is transferred to the outside world through the walls of the cup, but this transfer is blocked by the insulation. At the same time, because the air between the inner and outer layers is effectively isolated, the cold air from the outside cannot carry away the heat by conduction. In this way, the thermos cup can effectively maintain the temperature of the hot water.
The reason why the thermos cup can keep warm is mainly due to its good material, structure and thermal insulation principle. By blocking the transfer of heat and effectively maintaining the temperature of hot water, the thermos cup has become a good helper for us to keep warm in winter.
II,What are the key indicators for choosing a thermos cup?
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The key performance indicators of the thermos cup include holding time, sealing, drop resistance, ease of cleaning and appearance design. These performance metrics are detailed below.
1.Keep warm time.
Holding time is one of the important indicators to measure the performance of the thermos cup. A good thermos mug should be able to maintain the temperature of the water for a long time, so that people can enjoy a hot drink at any time when traveling, going to work, or outdoors. Generally speaking, stainless steel and ceramic thermos cups hold longer for a longer period of time, while plastic cups have a shorter holding time.
2.Tightness.
Tightness is an important indicator to measure whether the thermos cup is leaking. If the sealing of the thermos cup is not good, it will lead to hot water leakage, which will not only affect the heat preservation effect, but also bring inconvenience to the user. Therefore, when buying a thermos mug, you should pay attention to check its sealing performance.
3.Drop resistance.
Drop resistance is an important indicator to measure whether the thermos cup is durable and not easy to be damaged. If the user accidentally drops the thermos cup on the ground, it will cause the thermos cup to be damaged, which will affect its service life. Therefore, when buying a thermos mug, you should pay attention to its drop resistance.
4.Ease of cleaning.
Ease of cleaning is an important indicator to measure whether the thermos cup is easy to clean. If the inside or outside of the thermos cup is difficult to clean, it can lead to the growth of bacteria, which can affect the health of the user. Therefore, when buying a thermos mug, you should pay attention to its ease of cleaning.
5.Design.
Appearance design is an important indicator to measure whether the thermos cup is beautiful and generous. A good design can make users feel comfortable and happy, and at the same time, it can also improve the user's self-confidence. Therefore, when buying a thermos mug, you should pay attention to whether its appearance design meets your own aesthetic requirements.
When buying a thermos cup, you should choose a thermos cup that meets your own requirements according to your own needs and actual conditions. At the same time, attention should also be paid to the methods and skills of using and maintaining the thermos cup to prolong its service life and maintain good performance indicators.