Changing your outside doors with highly insulated and well draught-proofed doors will help keep your home warmer. Older external doors often fit poorly in their frames, letting cold draughts in and warm air out. A modern, high performance door will fit snugly and securely in its frame to keep the weather out. It will also be a good insulator, stopping heat escaping through the door itself. The door may be composite, wood, metal or PVC, often with insulation built into the structure.