Double Glazed Window Cracked Inside Patched May 2026

This is the "hot coffee in a cold mug" effect, scaled up. Imagine a bright winter morning: The outer pane is freezing. The inner pane, warmed by your central heating, wants to expand. But the outer glass holds the entire unit rigid via the spacer. The result? Tension builds in the inner pane until it yields. You’ll often see these cracks starting perpendicularly from the edge, then arcing.

This is the window industry’s hidden demon. Tiny, microscopic specks of nickel sulfide can be trapped in the float glass during manufacturing. Over years, these impurities slowly change crystalline structure, expanding by up to 4%. In a standard single pane, this causes a harmless chip. In a sealed, stressed IGU, it acts like a bullet from the inside. The crack often appears as a distinctive “figure eight” or butterfly shape, originating from a single point. double glazed window cracked inside

You touch the pane. It’s smooth. The crack is on the inside—but between the two sheets of glass. This is the "hot coffee in a cold mug" effect, scaled up