Energy-efficient window film works on heat transfer at the glass, the weakest point in most walls. Reducing solar heat gain eases the load on air conditioning through the warmer months, and some constructions also help with heat loss in a Dolton winter. Alongside that, the same layer filters UV and cuts glare, so the room becomes more comfortable to sit in as well as cheaper to condition. For homeowners weighing film against replacement glazing, film is the less disruptive route and keeps the existing frames and windows in place. What it delivers depends on the film chosen, the glazing already fitted and how the home is used, which is why the glazing should be identified before anything is specified.