Straw Bale Construction/Characteristics/Thermal mass
Thermal mass 
The interior plaster on a straw bale wall works as an excellent thermal mass on a diurnal cycle.
Thermal mass reduces temperature swings due to daytime warming and night time cooling, by absorbing and then gradually releasing heat. This can result in a direct reduction in the need for fuel or electricity to regulate temperature, and indirectly in savings through lifestyle adjustments: occupants of a moderate environment, with only gradual temperature swings, are less likely to use artificial heating and cooling. This is most easily achieved at high desert altitudes where a clear sky contributes to both warm days (solar gain) and cool nights (nighttime cooling), but the principle still works in other climates as well.