Six questions, one verdict. The thirty-second alcohol-wipe protocol that tells you whether your foggy window is a cleaning problem, a humidity problem, or a failed seal — before you spend three more bottles of cleaner.
Foggy windows look like one of several distinct patterns, and the pattern itself is part of the diagnosis. The intermittent cold-morning fog is a different failure from the milky cloudy residue that won't move, and the dark butyl smearing is a different failure from either. Look at the window in good light and pick the closest match.