Home & Kitchen · Head-to-head
3M Indoor Window Insulator Kit, Five Pack (2141W-6) vs Duck Brand Rope Caulk, White, 1/8 in. x 35 ft.
Which should you buy? Our verdict on both, pulled from our full The Best Window Insulation Kits: 4 Compared (and One to Skip) comparison.
The 3M kit covers the whole window with tight, clear film from the inside and comes off in spring. Duck's rope caulk is the cheapest way to plug the gaps around a sash and pulls back out when the season ends.
3M Indoor Window Insulator Kit, Five Pack (2141W-6)
Buy itHeat-shrink film on Scotch double-sided tape that turns a drafty window into a sealed pocket of still air for the winter.
- One box fits five 3 by 5 foot indoor windows, so a whole floor is covered by a single purchase.
- 3M says it saves energy, reduces condensation and prevents frost buildup, which targets both the draft and the cold-glass problem.
- The film shrinks tight with a hair dryer, and 3M says the tape works on painted, stained or varnished trim.
- 3M says not to apply the tape to painted walls, so windows with no trim around them are a poor fit.
- It is a seasonal fix, and you cannot open the window while the film is up.
- The film is thin and can be pushed off the trim; 3M advises light pressure even when cleaning it.
Duck Brand Rope Caulk, White, 1/8 in. x 35 ft.
Buy itA soft, paintable cord you press into the cracks around a window sash by hand and pull out again when you are done.
- Install is cut to size and press into place, with no caulk gun and no curing time.
- Duck says it will not stain or harden and lists it as removable and safe for renters and temporary living spaces.
- It is paintable, so it can be blended into trim on windows you seal for the whole winter.
- It only seals gaps; it does nothing for heat lost through the glass itself.
- The 35 foot roll is a small 1/8 inch cord meant for smaller holes, so wide gaps need a different product.
- The energy figure on the page is a general home-sealing estimate, not a test of this product.
Side by side
The 8 criteria below are the ones our full comparison judged every product on, narrowed to these two.
| 3M Indoor Window Insulator Kit, Five Pack (2141W-6) Our pick | Duck Brand Rope Caulk, White, 1/8 in. x 35 ft. | |
|---|---|---|
| Our verdict | Buy | Buy |
| Best for | Anyone with drafty or single-pane windows and wood trim who wants the most effective cheap fix this winter. | Renters and budget buyers whose windows leak air around the sash rather than through the glass. |
| Price tier | $ · budget | $ · budget |
| Type | Heat-shrink film and tape | Removable rope caulk |
| Where it goes | Inside, on the window trim | In gaps around the sash |
| Stops air leaks | Yes, seals the whole window | Yes, at the gaps it fills |
| Adds a still-air layer | Yes | No |
| Install | Tape, then shrink with a hair dryer | Cut and press in by hand |
| Coverage per package | Five 3 x 5 ft windows | 35 ft of 1/8 in. cord |
| Season or long term | One season | Remove when done |
| Warranty stated | 1 year limited | Not stated on page |
Which one is right for you?
Pick the 3M Indoor Window Insulator Kit, Five Pack (2141W-6) if
anyone with drafty or single-pane windows and wood trim who wants the most effective cheap fix this winter.
Know before buying: 3M says not to apply the tape to painted walls, so windows with no trim around them are a poor fit.
Pick the Duck Brand Rope Caulk, White, 1/8 in. x 35 ft. if
renters and budget buyers whose windows leak air around the sash rather than through the glass.
Know before buying: it only seals gaps; it does nothing for heat lost through the glass itself.
The bottom line
Our overall pick is the 3M Indoor Window Insulator Kit, Five Pack (2141W-6) - Heat-shrink film on Scotch double-sided tape that turns a drafty window into a sealed pocket of still air for the winter. Choose the Duck Brand Rope Caulk, White, 1/8 in. x 35 ft. instead if renters and budget buyers whose windows leak air around the sash rather than through the glass.
Want the full picture, including the other options we compared and the popular one we'd skip? Read the complete The Best Window Insulation Kits: 4 Compared (and One to Skip).