How to Fix a Double-Pane Window With Beads, Fog, or Moisture Between the Panes
When you see fog, haze, or tiny beads (desiccant) between the two panes of a double-pane window, the insulated glass unit (IGU) seal has failed. Warm air entered the space between the panes, depositing moisture — and the desiccant beads that used to absorb that moisture are now saturated and visible. This is a common issue in windows over 10–15 years old. The good news: you usually don't need to replace the entire window, just the glass unit.
Likely Causes
- 1Age — IGU seals typically last 10–20 years before the silicone or butyl tape degrades
- 2Temperature cycling causes the gas fill to expand and contract, stressing the seal
- 3Direct sunlight and UV exposure accelerating seal breakdown
- 4Physical damage to the frame allowing water infiltration
- 5Poor original installation leaving the seal vulnerable
This is not a structural emergency, but a failed IGU loses significant insulating value — raising your energy bills. Fix within a few months.
How to Fix It: Step by Step
- 1Confirm it's a failed seal
The fog or condensation is between the two panes — not on the interior surface (from room humidity) or the exterior surface (from outdoor dew). If you can wipe it off, it's just surface condensation. If it's trapped inside the glass sandwich, the seal has failed.
- 2Measure the IGU
You'll need the exact size to order a replacement. Measure the width and height of the glass unit itself (not the frame opening). Also note the total thickness of the unit — typically 5/8", 3/4", or 1" — and whether it has Low-E coating (a slight blue or green tint).
- 3Decide: IGU replacement vs. full window replacement
If the frame is in good condition (no rot, still opens and closes well, no air leaks around the frame), replace just the IGU. If the frame is damaged or the window is very old with poor performance, full replacement may make more sense long-term.
- 4Order a replacement IGU
Order from a local glass shop or online IGU supplier. Provide the exact dimensions and thickness. Standard lead time is 5–10 business days. Argon-filled Low-E units cost more but restore the original energy performance.
- 5Remove the window sash
Most double-hung windows have sashes that tilt in or lift out. Tilt the sash inward (press the tilt latches at the top) and lift it out. Lay it flat on a padded work surface.
- 6Remove the glazing stops and old IGU
Glazing stops are the thin strips of vinyl or wood holding the glass in the sash frame. Pry them out carefully starting at a corner using a stiff putty knife. The IGU will slide or lift out once all stops are removed.
- 7Install the new IGU
Clean the sash frame. Place setting blocks (small rubber pads) at the bottom corners of the frame to support the glass. Slide the new IGU in. Reinstall the glazing stops, pressing them firmly until they click or snap into place.
- 8Reinstall the sash
Tilt the sash back into the window frame and click it into place. Open and close the window to verify operation. Check that the new IGU is clear with no condensation.
Materials & Tools Needed
Warning Signs It's Getting Worse
- ⚠Foggy area spreading across more of the window over time
- ⚠Visible mold or dark staining inside the IGU space
- ⚠Frame feels soft or spongy (water has reached the wood frame)
- ⚠Multiple windows fogging simultaneously (may indicate ventilation issue contributing to excess humidity)
When to Call a Professional
Call a glass shop or window installer if: the sash doesn't tilt in (older windows may require full frame removal), you can't source the right IGU size, the frame itself has rot or damage, or you have specialty glass (tempered, laminated, or obscure glass) that needs exact matching.
Not sure where to start?
Describe your problem and get a personalized repair plan — likely causes, repair steps, materials, and cost estimates.
Get My Repair Plan