More than 60% of the heat loss of the SunCatcher is through the south facing glazing and about 2/3 of that occurs at night when the structure is cooling. This is due in part to heat loss by radiation (like a camp fire or woodstove). An insulated reflective curtain can cut night time heat loss through the glazing by more than 50%. During the cold winter months closing the curtain at night will increase the temperatures inside the SunCatcher when it is most needed. In moderate climates the curtain is probably not necessary. In very cold climates it is required.