Will Solar Film Stop Heat Loss in Winter

Simple answer is no. Although solar films provide medium to high heat rejection in summer, they provide little, if any, heat retention in winter. The heat rejected in summer is mainly in the form of direct, and reflected sunlight; whereas in winter the heat lost through windows is radiant heat in the infra-red spectrum. The best way of reducing heat lost through windows in winter is either by the use of double glazing, or by the use of heavy/thick curtains or drapes.