The insulation and cold preservation principle of vacuum bottles (thermos flasks/cups) is based on blocking the three modes of heat transfer-conduction, convection, and radiation. Its core structure consists of double-walled containers (usually glass or stainless steel) with a vacuum between them.
The vacuum state virtually eliminates the air medium, effectively preventing heat conduction and convection. Simultaneously, a reflective layer such as silver or aluminum is plated on the outer side of the inner wall to reflect heat radiated from the inside (or heat flowing inwards from the outside), significantly reducing heat exchange caused by radiation. A well-sealed stopper or lid further reduces heat loss through convection. Therefore, this principle applies not only to maintaining high temperatures (insulation) of the internal liquid but also to maintaining low temperatures (cold preservation).
