dish. Seriously. It's an old dritbike/snowmobubble trick ( that I myself just heard this past winter).
Put soap in a dish in the shower. Take the nasty gel-like substance it leaves in the bottom and rub it on the inside of the lense. Let it dry then wipe off. Worked for me this winter when just the antifog mask/gaurd my helmet came with wouldn't stop fogging at slow speeds. The soap + mask = no fogging at any speeds. You might need to redo it every few months, but I never have.
