 When this radiation strikes the dark colored surface of the thermal mass facing the sun, the energy is absorbed and then re-emitted in the form of longer-wavelength radiation that cannot pass through the glazing as readily.Hence heat becomes trapped and builds up in the air space between the high heat capacity thermal mass and the glazing that faces the sun.Another phenomenon that plays role in the Trombe wall’s operation is the time lag caused by the heat capacity of the materials.