Your average Science teacher will tell you the dreaded wet window fog will appear when lovely warm air meets an inviting cold surface.
And along with dirt and grime, it's probably the one visible exterior 'thing' that can make bus travel seem instantly less attractive. Windows you can't see out of makes a bus look cold, damp and uninviting - hardly an image the industry is striving for.
Common sense says a bus will look more attractive on a hazy summer's day with the sun bouncing off those RAL colours than it ever will on a wet Wednesday in December.
It's just a fact of life that buses will always look dirtier in winter, and apart from cleaning the exterior daily and avoiding muddy puddles, there's only so much an operator can do.
The long-term solution to condensation is to get the best, double glazed windows you can afford. Although it's doubtful you can eliminate condensation totally, speccing the most effective glazing in the first place will give you a better chance of making sure customers have a decent view in cold weather.
When you've got a product that spends its day being showcased to potential customers, you've got to do everything in your power to make it look like it competes with the alternative.