Winter windows | Updated October 2026
Your heat is
Your heat is
escaping through
the windows?
Window insulation film
is just right.
The short version…
- About 58% of the heat lost in winter goes out through windows and other openings
- Film adds a layer of air that cuts the chill and condensation
- Some glass can't take film — wired and double glazing. Check first
Measure your windows: how many sheets you need
Time for Choudo-kun, our tape measure. Measure just the glass (not the frame) and enter the width and height. We calculate for common 90 × 180 cm and 90 × 230 cm sheets.
Area to cover-
90 × 180 cm-
90 × 230 cm-
For each pane we cut as many 90 cm-wide strips as needed; short panes get two or more strips from one sheet. Trimming waste and re-dos aren't included, so buy one extra. Sheet sizes from Nitoms "Window Glass Insulation Sheet" specs (about 90 cm × 1.8 m / 2.3 m).
Measure only the visible glass. While you're there, check for a wire grid and whether there are two layers of glass.
Our picks by type
Choose by your glass type and how much view you want to keep.
A: Keep the view (clear, water-applied)
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- About 2 mm, clearer type
- Applied with water, peels off easily
- For single clear panes
B: Warmth first (thick foam)
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- About 3.5 mm air layer
- For bedrooms and north-facing windows
- Use long rolls on big windows for fewer seams
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Who it suits — and who it doesn't
○ Good for you if…
- It's chilly near the window and the heating struggles
- Your windows are dripping with condensation in the morning
- You rent and want to fix cold windows without any work
- Your windows are single panes of clear, smooth glass
× Not for you if…
- Your windows are wired glass, double glazing or Low-E glass
- You want a crystal-clear view (it looks a bit frosted)
- Drafts through the frame are the real problem
- You want a real upgrade (consider inner windows or replacement)
Insulation film doesn't add heat — it keeps in the heat you've paid for. It helps whatever heater you use.
How it works, and glass you shouldn't cover
A single pane of glass is thin, so room heat passes straight through. Insulation film adds a layer of tiny air pockets, like bubble wrap, on the inside of the glass. The inner surface stays warmer, so condensation forms less, too.
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Glass you shouldn't cover (thermal stress cracks)
When sun hits the glass, the covered part and the part hidden in the frame can reach very different temperatures, and the glass can crack — a thermal stress crack. Glassmaker Nippon Sheet Glass warns that film or paper on glass can cause this. Before applying film to the glass types below, check the product's instructions.
| Glass | How to tell | Insulation film |
|---|---|---|
| Single clear pane | Smooth, one layer | Most films are OK |
| Wired glass | A wire grid inside | Cracks easily — only use film made for it |
| Double glazing | Two panes with a gap | Risk of cracking — only use film made for it |
| Patterned (frosted) glass | Bumpy on one side | Water-applied film won't stick to the bumpy side — use a type for patterned glass |
5 tips for choosing
-
First, check what glass you have
Wired, double-glazed and Low-E glass can crack. Always check "suitable glass" on the package or instructions. -
Renting? Choose a water-applied type
It sticks with water, no adhesive, so it comes off easily (Nitoms says it "goes on neatly and comes off neatly"). -
Choose by thickness
A thicker air layer slows heat more. Nitoms, for example, sells a clearer ~2 mm type and a ~3.5 mm foam type. Thinner keeps more of the view; thicker is warmer. -
Bumpy glass needs a patterned-glass type
Water-applied film won't stick to the bumpy side of frosted (patterned) glass. Use an adhesive type made for it. -
Tall windows: long sheets or rolls
For floor-length windows taller than 180 cm, a 230 cm sheet or a long roll means fewer seams. Check the count with the tool above.
Common mistakes
Mistake: putting film on wired glass without checking
Instead: it may crack. On wired or double glazing, only use film made for it
Instead: it may crack. On wired or double glazing, only use film made for it
Mistake: it's still cold by the window after applying film
Instead: cold air also gets in through the frame and gaps. Add floor-length thick curtains or draft-stopper tape
Instead: cold air also gets in through the frame and gaps. Add floor-length thick curtains or draft-stopper tape
Mistake: a heater in front of the window, blowing hot air on the glass
Instead: heating one part of the glass can cause cracks. Glassmakers warn not to blow heating or cooling air straight at glass
Instead: heating one part of the glass can cause cracks. Glassmakers warn not to blow heating or cooling air straight at glass
Mistake: applying it to dirty glass, so it peels right off
Instead: wipe the glass first to remove dust and grease
Instead: wipe the glass first to remove dust and grease
Good to know if you live in Japan
-
Search in Japanese
Window insulation sheet is 窓 断熱シート; water-applied is 水貼り; wired glass is 網入りガラス; double glazing is 複層ガラス or ペアガラス; patterned glass is 凹凸ガラス or 型板ガラス. -
Renting: keep it removable
Leaving marks on the glass could become a cost when you move out. Water-applied types are the safer choice; ask your landlord or management company if you're unsure. -
Sizes are in centimeters
Sheets are usually 90 cm wide. Measure in centimeters before you shop.
FAQ
Can I use bubble wrap from packaging instead?
It adds an air layer, so it helps somewhat. But packaging bubble wrap is usually one-sided, and taping it up can leave marks on the glass. Window insulation sheets are mostly water-applied, with the air layer sealed between two films, so they look better and are easier to fit. Don't put it on wired glass either.
I applied it but can't feel a difference
Three common reasons: cold air through the frame and gaps (add curtains or draft tape), the sheet is thin (choose a thick foam type), and only part of the glass is covered (cover the whole pane).
What about summer?
Winter sheets can make glass heat up more in strong summer sun, and thermal stress cracks happen most on sunny windows. Peel them off when winter ends, or choose a product labeled for summer and winter.
Which heater is right for you?
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