A double-walled glass consists of two layers of glass, an inner layer and an outer layer, separated by an interlayer. This interlayer can be a vacuum layer or an air layer, but for safety and manufacturing reasons, the middle layer of most double-walled glasses is not completely vacuum-sealed; it contains gas and has a sealing hole at the bottom of the outer layer.

The vacuum or air layer effectively blocks heat conduction and convection, thus slowing down the heat exchange between the liquid inside the glass and the external environment. This prevents the outer layer of the glass from heating up rapidly, providing insulation and preventing burns; it also slows down heat loss from the inside of the glass, providing a certain degree of heat preservation. Its heat preservation effect is worse than that of ordinary single-walled glass cups, but the heat preservation time is usually not as long as that of professional vacuum insulated containers (such as stainless steel vacuum insulated cups). Its main functions are "heat insulation and burn prevention" and "general heat preservation."