A failure in the seal of a double-paned window allows moisture to enter in amounts that are too large for the absorbent silica pellets in the window to prevent. Double-paned windows have a layer of gas between the two panes. Constant expansion and contraction of this gas as temperature fluctuates throughout the day places stress on the seal, causing it to fracture.
Some windows are more vulnerable to seal failure and the resulting moisture between the panes. Windows on the sunny side of a house experience more extreme fluctuations in temperature, resulting in more expansion and contraction. Vinyl windows have a higher failure rate, while some batches of windows contain manufacturing defects that cause the seals to fail.
Riverbedding and silica haze are two results of moisture condensing on the inside of double-paned windows. When water condenses and runs in narrow paths carving grooves into the window it is called riverbedding. Silica haze occurs when the silica pellets erode and accumulate on the window surface.
Condensation may not always occur when a window seal fails. In this case, infrared cameras can be used to record differences in temperature and detect failure. Replacement of the glazing assembly, sash or entire window is often necessary, depending upon the severity of the problem.