Best Expanding Foam Sealant for Air-Sealing Gaps (2026)
By Nate Sawyer, Editor · Updated July 2026
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Spray foam is the fastest way to air-seal gaps, penetrations, and rim joists, but the wrong formula can bow a window jamb. We split our picks by job: high-expansion for big voids, low-expansion for frames. Prices are approximate US street prices.
A high-expansion polyurethane foam that quickly fills large, irregular voids up to 3 inches, ideal for rim joists, penetrations, and pest-blocking. The closed-cell foam adds R-value and blocks air and drafts cheaply. Cautions: it expands aggressively and can bow window or door jambs in tight frames, and cured foam is nearly impossible to remove.
- Air sealing
- Filling large gaps
- Pest blocking
Pros
- High expansion fills big voids fast, so one can covers a lot of rim-joist and penetration sealing
- Closed-cell foam adds real R-value and blocks air, drafts, and small pests
- Cheapest way to seal large irregular gaps compared with backer rod plus caulk
Cons
- Expands aggressively and can bow window/door jambs if used in tight frames
- Sticky and nearly impossible to remove from skin, clothing, or trim once it cures
- Straw can clog after one session, so leftover foam in the can is usually wasted
A low-expansion polyurethane foam made for the gap between a window or door frame and its rough opening. Its minimal expansion seals and insulates without bowing the jamb or binding the sash, and it stays flexible for seasonal movement. Limits: it is not for gaps over 1 inch, costs a bit more than Gaps & Cracks, and still cures permanent.
- Drafty windows
- Drafty doors
- Air sealing
Pros
- Low-expansion formula seals frame gaps without bowing the jamb or binding the sash
- Stays flexible after curing so it tolerates the seasonal movement of window and door frames
- Dispenses in most orientations, making overhead and sideways frame gaps easier to fill
Cons
- Not for gaps over 1 in, so wide rough openings need backer rod or multiple passes
- Costs a bit more than the standard Gaps & Cracks version for the same can size
- Still cures sticky and permanent, so overfill mistakes are hard to clean up
A high-density polyurethane foam for air-sealing and filling gaps up to 1 inch, indoors or out. It dries a bright, paintable white that blends with trim, goes tack-free in about 8 minutes, and its UV-resistant density beats budget foams outside. Keep in mind it is rated only to 1-inch gaps, and the white yellows somewhat if left unpainted in sun.
- Air sealing
- Filling gaps
- Exterior sealing
Pros
- Dries a bright white that blends with trim and is easy to paint over, unlike orange/yellow foams
- Fast tack-free time of about 8 minutes speeds up multi-spot sealing jobs
- High-density, UV-resistant foam holds up better than budget foams on exterior use
Cons
- Rated only to 1 in gaps, so it is not a substitute for a big-gap or 3 in foam
- White color still yellows somewhat with long UV exposure if left unpainted
- Like all straw-applied cans, the tube clogs and the remainder is usually one-and-done
Still deciding? Compare them
Frequently Asked Questions
- What is the difference between gaps-and-cracks foam and window-and-door foam?
- Gaps-and-cracks foam expands aggressively to fill large voids up to about 3 inches, while window-and-door foam is a low-expansion formula that seals frame gaps without pushing the jamb out of square. Use low-expansion foam around any window or door.
- Is expanding foam paintable?
- Yes, most polyurethane foams are paintable once fully cured. Trim off the excess with a knife, sand it flush, and prime before painting. Loctite Tite Foam cures white, which hides better under paint than orange or yellow foams.
- Can I reuse a can of spray foam after opening it?
- Straw-applied cans usually clog after one session, so plan to use most of the can at once. Gun-applied (PRO) cans can stay attached to the gun and be reused for weeks, which is why pros prefer them for repeat work.