Glossary
Draft stopper
A foam or fabric seal placed along a door or window gap to block cold air without any permanent installation.
A draft stopper is a foam strip, fabric tube or adhesive seal placed along the gap under a door or around a window frame to block outside air from leaking in. Unlike caulking or weatherstripping that's screwed or nailed into the frame, most draft stoppers sold for rentals rely on pressure, adhesive backing or simple weight, so they come off without altering the window or door.
The gaps that matter most are usually the bottom of exterior doors, the meeting point where a window sash closes, and any visible daylight around an old frame, all of which let conditioned air escape and outside temperature in regardless of how well the heater or AC is working.
Draft stoppers are a small, low-cost fix compared to a full window insulation kit, but they work best combined with one rather than instead of it. Sealing the biggest, most obvious gaps with a draft stopper first, then adding an insulating film or kit to the whole window if drafts persist, gets most of the benefit without a large upfront cost.