Anti Fog Visor Systems. I have tried many options, but latest one (and the most expensive) is PINLOCK visor, made in Netherlands. Some helmets have a pre-fitted option for these, others have a self-fitting kit. I used the self – fitting kit for the Shark S800 helmet. It is unrivalled — no foggging at all, ever — since fitting. Tested in 2hrs + of pouring rain, central Nth Island going to Flock Hill Rally, in the dark! No NZ distributor, though – but the website gives contact in Oz, and the distributor is very helpful, product arrives within a week. http://www.pinlock.com/default1.asp
Hope you find what works!
Cheers, Peter ST 🙂