There are three methods of heat transfer: thermal radiation, heat conduction, convection.

Insulated cup is mainly to solve the first two kinds of heat transfer caused by the heat loss.

Insulation mug vacuum sandwich effectively suppress the occurrence of heat conduction (under vacuum, there is no transfer medium)

At the same time, we will find that the inner layer of the thermos cup is silver and can be reflective, which mainly reflects the heat energy transmitted by the thermal radiation (the heat is actually a short-wave radiation that can be reflected back as light)