A thermoflask minimizes both heat loss and heat gain through a combination of design features that target the three modes of heat transfer: conduction, convection, and radiation. Heat Loss (from a hot liquid inside): 1. Conduction: Heat from the hot liquid conducts through the inner glass wall. The vacuum between the inner and outer walls is a very poor conductor, so very little heat is conducted across this gap to the outer wall. The stopper is made of a material that is a poor conductor, limiting heat transfer through the opening. 2. Convection: Convection currents within the liquid transfer heat to the inner wall. The vacuum prevents convection currents from forming in the air gap, so heat cannot be transferred by air movement between the inner and outer walls. The stopper seals the opening, preventing air from circulating in and out of the flask. 3. Radiation: The hot liquid emits thermal radiation. The silvered surfaces of the inner wall reflect most of this radiation back into the liquid, significantly reducing heat transfer by radiation across the vacuum gap. Heat Gain (from a cold liquid inside): 1. Conduction: Heat from the surroundings conducts through the outer wall. The vacuum gap significantly slows down conduction to the inner wall. The stopper also limits conduction from the outside air. 2. Convection: Convection currents in the outside air transfer heat to the outer wall. The vacuum prevents convection currents from carrying heat to the inner wall. The stopper prevents air from entering the flask, which would transfer heat by convection. 3. Radiation: The surroundings emit thermal radiation. The silvered surfaces of the outer wall reflect most of this external radiation away from the flask, preventing it from reaching the cold liquid inside.