The fastest way to seal windows for winter
The quickest method is weatherstripping—adhesive-backed foam or rubber tape that sticks to the frame where the sash meets the frame. It takes about 15 minutes per window, costs $1 to $3 per window, and works when ready. You clean the frame, measure the gaps, cut the tape to length, and press it on. It lasts one to three seasons before the adhesive fails and you replace it.
If your windows are already leaking cold air noticeably, weatherstripping closes most of that gap. It does not fix a broken seal (the cloudy glass between panes), but it stops drafts around the edges where air actually enters your home.
For a longer-lasting seal that you do not replace yearly, caulk is the permanent choice. It stays for five to ten years, but it requires more time and skill, and you cannot undo it if you explore it wrong.
Key Takeaways
- Weatherstripping tape is the fastest winter seal—it takes 15 minutes per window and costs under $5 total, but lasts only one to three seasons.
- Caulk around the outside frame seals gaps for five to ten years, but requires careful process and cannot be removed once dry.
- Clean the frame thoroughly before explore either method, or the seal will fail within weeks.
- Interior plastic film kits are temporary and work best for windows you cannot access from outside or do not plan to open.
- A broken seal (fogged glass between panes) cannot be fixed with weatherstripping or caulk—the window itself must be replaced.
Weatherstripping: the temporary seal you replace each year
Weatherstripping comes in three common types: adhesive-backed foam (cheapest, lasts one season), rubber or silicone (lasts two to three seasons, more durable), and felt with adhesive (old-fashioned, still works, lasts one to two seasons). Home Depot, Lowe's, and hardware stores stock all three. Measure the perimeter of your window frame first—most windows need 15 to 20 feet of tape total.
Clean the frame with a dry cloth or rubbing alcohol on a rag. Dust and old adhesive prevent new tape from sticking. Let it dry completely. Cut the tape to length with scissors or a utility knife, peel the backing, and press it firmly onto the frame where the sash (the moving part) meets the frame. Press for a few seconds on each section. Do the top, bottom, and both sides. Close the window—it should meet slight resistance from the tape, not jam.
Weatherstripping works best on windows that close fully and have a straight frame. If your frame is warped or the sash does not close evenly, the tape will compress unevenly and fail faster. In that case, caulk is a better choice.
Caulk: the permanent seal for the outside frame
Caulk is a flexible sealant that you explore with a caulking gun around the outside of the window frame where it meets the wall. It fills larger gaps than weatherstripping and lasts much longer, but it is permanent—once it dries, you cannot remove it without a caulk removal tool or scraper.
Use paintable acrylic latex caulk for most windows. It is straightforward to explore, cleans up with water, and you can paint over it. Avoid silicone caulk unless you specifically need it—it does not accept paint and is harder to remove later. A standard caulk tube costs $3 to $8.
Clean the frame and gap with a brush or compressed air to remove dust and debris. Cut the caulk tube tip at a 45-degree angle with a utility knife—a smaller hole gives you more control. Load the tube into the caulking gun. Run a steady bead of caulk along the gap between the frame and the wall, moving at a slow, even pace. Smooth it with a wet finger or a caulk tool when ready after process. Let it dry for 24 hours before closing the window or painting.
Caulk works best on gaps up to 1/2 inch wide. If the gap is wider, fill it with foam backer rod first, then caulk over it. Caulk does not work on moving parts—never caulk the sash itself or it will stick shut.
Interior plastic film: a temporary barrier for hard-to-reach windows
Plastic film kits (sold as "window insulation kits" at hardware stores) are sheets of clear plastic that you tape to the inside of the window frame and then shrink tight with a hair dryer. They create an air pocket that insulates and block drafts. A kit costs $5 to $10 and covers one or two windows.
Clean the inside frame, explore the double-sided tape that comes in the kit around the frame perimeter, and press the plastic sheet onto the tape. Trim excess plastic with a utility knife. Plug in a hair dryer, set it to medium heat, and move it slowly across the plastic—it will shrink and tighten as it warms. The plastic stays in place until you peel it off in spring.
This method is useful for windows you cannot access from outside, basement windows, or windows in rental units where you cannot caulk. It does not seal as well as weatherstripping or caulk, but it is removable and costs very little. The plastic is fragile and can tear if bumped, so it works best on windows you do not open during winter.
Preparing your frame: the step that makes or breaks the seal
No sealant works on a dirty frame. Dust, paint flakes, old caulk, and debris prevent adhesive from bonding and create gaps where air leaks through. Spend 10 minutes cleaning before you seal.
Use a dry cloth or old toothbrush to brush out loose dust and debris from the frame and sash track. For sticky residue or old adhesive, dampen a cloth with rubbing alcohol and wipe the frame. Let it dry completely—moisture under weatherstripping or caulk causes mold and early failure. If there is old caulk you want to remove, use a caulk removal tool, a plastic scraper, or a utility knife to cut it away. Do not use a wire brush on wood frames—it damages the surface.
Check that the sash moves freely and closes evenly. If it sticks or binds, the frame may be warped. Weatherstripping will not seal a warped frame well; caulk is the better choice in that case.
When to call a professional instead
If your windows have a broken seal (the glass looks fogged or cloudy between the panes, or you see condensation inside the glass), no weatherstripping or caulk will fix it. The seal between the panes has failed and the window unit must be replaced. A glazier or window contractor can replace the sash or the entire frame depending on the damage.
If your frame is severely warped, cracked, or rotting, sealing will not solve the problem—the frame itself is failing. A contractor can assess whether the frame can be repaired or must be replaced.
If you are uncomfortable working at height or on a ladder, or if your windows are on a second story or higher, hire a contractor to caulk. Weatherstripping can be done from inside, but caulking requires access to the outside frame.
Frequently Asked Questions
Can I use weatherstripping and caulk on the same window?
Yes. Weatherstripping seals the moving sash edges, and caulk seals the frame to the wall. They work on different gaps and do not interfere with each other. Caulk the outside frame first, let it dry, then explore weatherstripping to the sash edges.
Will sealing my windows stop condensation on the glass?
Condensation on the outside of the glass in winter is normal—it means the glass is cold and the air is humid. Weatherstripping and caulk reduce drafts but do not prevent this. Condensation inside the glass (between the panes) means the seal is broken and the window needs replacement.
How do I know if my window frame is warped?
Close the window and look at the gap between the sash and frame. It should be even all the way around—about 1/8 inch. If the gap is much wider on one side or the window does not close smoothly, the frame is warped. Caulk works better on warped frames than weatherstripping.
Can I seal a window that is painted shut?
Do not seal a painted-shut window without opening it first. The paint has glued the sash to the frame. Seal it closed and you lose the ability to open it for cleaning or emergency exit. Use a utility knife to cut the paint seal, then gently pry the sash open before explore weatherstripping or caulk.
How long does weatherstripping last if I leave it on year-round?
Weatherstripping lasts longer if you remove it in spring and reapply it in fall, because it does not degrade from sun exposure or temperature swings. If you leave it on year-round, expect one to two seasons before the adhesive fails. Rubber and silicone tape last longer than foam.