 So, if there is enough mass, the wall can act as a radiant heater all night long.On the other hand, if the mass is too thick, it takes too long to transmit the thermal energy it collects, thus, the living space does not receive enough heat during the evening hours when it is needed the most.Likewise, if the thermal mass is too thin, it transmits the heat fast, resulting in overheating of the living space during the day and little energy left for the evening.