Weatherproof (weatherize) a window in three places: the opening sash (fit a compressible weatherstrip – EPDM foam D or P profile for casements, wool pile for sliding windows), the fixed joints between frame and wall (caulk), and the glass edge (replace hardened glazing gaskets). Start with a draught test so you fix the gap that actually leaks.
IllustrativeFind the leak first
- On a windy day move a lit incense stick or a strip of tissue around the closed sash.
- Close the window on a sheet of paper at several points – if it slides out easily, the seal is not touching.
- Look for daylight around the frame and for cracked caulk outside.
Which fix for which gap
| Where | What to use | Note |
|---|---|---|
| Opening casement / tilt-turn sash | EPDM foam D, P or E strip, self-adhesive | Seals when compressed; replace every few years |
| Sliding window or door | Wool pile (brush) weatherstrip, often with a fin | Lets the sash slide while blocking draughts |
| Fixed joint frame-to-wall | Exterior caulk / sealant | Not a weatherstrip job |
| Glass to frame | Glazing wedge or bulb gasket | Replace when hard or shrunk |
| Single-glazed, winter only | Removable film kit | Temporary |
Choosing the strip size
Measure the gap with the window closed. Choose a strip slightly taller than the gap so it is squeezed: I (9 × 2 mm) and E (9 × 4) suit thin, even gaps; P (9 × 5.5) and D (9 × 6 and up) suit larger or uneven gaps. See the foam profile size chart.
For retailers and installers
Foam strips are supplied in black, white, brown, grey and beige on rolls; 100 m or 150 m rolls, usually 4 rolls per carton, or retail packs on request. Orders start from 10 m.
Quick questions
Is weatherstripping or caulk better for windows?
They do different jobs: weatherstrip seals the moving sash, caulk seals fixed joints. Most drafty windows need weatherstrip first.
How long does window weatherstripping last?
Foam strips usually need replacing after a few years of use; EPDM keeps its spring longer than PU or PVC foam. Replace when it stays flat or cracks.
Need a seal for this?
Send your section, gap size or a photo of the old seal – Dora replies usually within 2 hours. Door & window seals are available from 10 m.