Weatherstripping
The seal around doors and windows that blocks drafts and air leaks.
Weatherstripping is the flexible foam, felt, or rubber seal that closes the gap around movable doors and windows. When it wears out, conditioned air escapes and outside air leaks in — raising your energy bills and hurting comfort. It's cheap to replace and one of the most cost-effective efficiency fixes in a home. Check it each season and replace any that's cracked or compressed.