The bad news first: You cannot "repair" the fog. That milky film between the panes is condensation from humid air that has infiltrated the failed seal. No amount of DIY drilling, chemical drying agents, or defogging kits will restore the window’s original insulating power. At best, they offer a temporary cosmetic fix; at worst, they can crack the glass.
Roughly 10% to 50% of the cost of a full window replacement. Note that while this restores clarity, it does not always restore the full original R-value (insulation). 2. Replacing the IGU (The Best DIY Fix) fixing double pane windows
A handful of companies offer a service where they drill a tiny hole in the glass, spray a cleaning solution inside, vacuum out the moisture, and insert a one-way valve. This removes the fog, but it does not replace the lost insulating gas. Your window will become a single-pane unit with a tiny hole. The fog may return in 1-3 years. The bad news first: You cannot "repair" the fog
You’ll find YouTube videos showing you how to drill your own holes. Resist the urge. You can temporarily clear the fog, but you’ll permanently damage the window’s structural integrity, void any remaining warranty, and likely shatter the glass. At best, they offer a temporary cosmetic fix;
Over time, the airtight seal that holds the insulating gas (like argon) can degrade. This leads to fogging or condensation that you can't wipe away because it's between the two panes of glass.
Air leaking around the edges, often caused by damaged frames or old weatherstripping. 🔧 Repair Strategies Replacing the Glass Unit (IGU)