I have Scorpion Helmets which come standard with a fog-free coating, but I also keep Fog-Tech (
http://www.amazon.com/FogTech-Anti-f.../dp/B001JR4CIO) in my tank bag for really foggy days. If you don't have a shield with ant-fog properties, I used to use Fog-City inserts (
http://www.webbikeworld.com/motorcyc...ty-progrip.htm) with great success for rainy/wet mountain riding.