So who drives a motorcycle and hasn't had problems with a foggy visor ? I thought I should sum up the best solutions here. It's all about reducing the surface tension of the minuscule waterdrops which the fog is made of. When this surface tension is reduced, the fogging effect is reduced.
1. Shaving cream: apply a thin layer of shaving cream to the inside of the visor. Be sure that you don't push it into the vents. Wipe clean with a dry cloth. It's actually possible to get a clean visor, without smudges. Use the inside of a sweats
hirt (soft). Works, but when standing still the damp builds up to an oil-like film in parts of the visor. The damp dries quickly when driving away. Not as bad as fog, but still. This is still a good solution for glasses, even though it creates a slight lens flare effect. Works in speeds from 30 km/h upwards.
2. Dish washing liquid: apply to inside of visor and let it dry. Wipe clean with dry cloth. Should be as effective as the shaving cream. Haven't tried it myself.
3. Pinlock: damp absorbing plastic that you need to screw on to your visor. Seems like a more permanent solution. You need to drill two holes in your 100€ visor which can scare some people. Check out the WebBikeWorld review for this piece of kit.
4. Fog City or ProGrip visor inserts. See the WebBikeWorld review. Some say that damp builds up like an oil film when breathing heavily (read: not perfect, might as well stick with shaving cream)
5. Respro Foggy Mask: Neoprene breath guard, comes recommended. Just bought a couple of these babies. I hope this saves me the trouble of using butter on my glasses.
6. There are a number of other sprays, impregnated cloths, etc, of which a small number work more or less. Try on your glasses before you buy ;)
Picture: Respro Foggy mask