A special energy-saving film can be glued, both on plastic and simple windows, such a film will give approximately 20-30% of the safety of heat, but not more. It is better to entrust such a film to the specialist. The use of plastic windows can be considered the most worthy method for saving heat in the house. Drilling manufacturers add various spraying to glass, create a vacuum between the glasses, and in some cases fill with special gas. And this is done to reduce heat loss. Which should remain in the apartment, and not heat the street. And what glass, how much heat will save you can read by choosing a double -glazed window. Anyone who says that double -glazed windows do not keep warm, just does not know what he is talking about.