I tried an anti fog visor insert last weekend. It worked great and I would highly recommend it to anyone as a cheap safety insurance when racing in damp conditions.
Before I had it, my helmet would fog up during rainy days. It seemed to make it worse if I opened up the helmet's vents, because of more moist air pushed in at high speeds at the end of the straights.
Here's a link and reviews. They get good rating for their anti fog performance, but don't seem to last very long.
$0.02
http://www.webbikeworld.com/motorcyc...ty-progrip.htm
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