The outer shell of a thermos flask is made of materials such as bamboo weaving, plastic, sheet metal, aluminum, and stainless steel. It has a rubber gasket at the mouth and a bowl-shaped rubber base at the bottom; these are used to secure the glass liner and prevent it from colliding with the outer shell.
The area around the neck of the thermos flask is where its heat retention is weakest, as heat is mostly conducted away there. Therefore, manufacturers strive to shorten the neck as much as possible. The larger the capacity and the smaller the neck, the better the insulation. Under normal circumstances, it can keep cold drinks at around 4°C and boiling water at around 60°C for up to 12 hours. Thermos flasks are closely related to people's work and daily life. In the home, they are often used to store hot water for daily drinking or entertaining guests. In laboratories, they are used to store chemicals; during picnics and football matches, people use them to store food and drinks; and in outdoor work and road trips, they are often used to carry and maintain the temperature of drinking water and iced drinks. In recent years, many new designs have been added to the spouts of thermos flasks, resulting in pressure thermos flasks and contact thermos flasks, but the principle of heat preservation remains the same. Furthermore, modern thermos flasks can hold various beverages such as tea, coffee, juice, and milk, and their reusable nature helps reduce the consumption of disposable containers, aligning with environmental protection principles.