ooo, Big questions man!
1.) First, let's consider mod/rigid full face helmets. Modular helmets are unable to be SNELL rated due to their design and the way SNELL is certified. Something to consider. However, that's OFF TOPIC, so, I'll let you create another thread, or find a SNELL/DOT discussion thread to post on about that. What is relevant to this topic though is that full face helmets don't have as many random air leaks as modular helmets. When eliminating fog, you want to control the airflow in your helmet as best you can. I would recommend a regular, rigid, full face. I'm very happy with my Shoei RF-1100.
2.) Helmet Fogging - I have ridden down to -17F and in any weather condition imaginable. So, if you're planning to ride in colder than that, you'll have to do your own experiments.... However, this is what I've learned. Your face shield/glasses fog up because of your breath.
First line of defense against fog:
Respro: Racing - Road Racing - Foggy Mask - just about the coolest thing since sliced bread when it comes to fogging. Keep your breath away from your visor/glasses and they won't fog up. I've found that when getting close to 0F your eyes actually emit enough heat to fog up your glasses, but not your visor.
Second line of defense against fog on your visor:
Pinlock Original | Pinlock - pretty much the second coolest thing since sliced bread. It worked great down to about -10F at which point my breath was exiting the bottom of the helmet and icing on the OUTSIDE of the visor - where I used by built in ice scraper on the Winter Elite gloves to get rid of it.
Second line of defense on your glasses:
Ek 123625 Cat Crap Anti-Fog: Amazon.com: Sports & Outdoors
Zooke Products - Anti fog spray for glasses
and other some such treatments for sea-through anti-fogging protection.
These things aren't nearly as cool as sliced bread, but they work, sort of... How do they work? Well first, what is fog on a lens? It's microscopic droplets forming over a surface. If this surface is transparent, it refracts all the light rays which our eyes use to interpret the picture we see into a confusing mess. These treatments fill in the microscopic cracks in the transparent surface, and creates a barrier over the top of it that is super slick, so water vapor doesn't have the ability to stick in the form of droplets. Essentially it's creating a surface slicker than the capillary action of water can hold on to. However, this doesn't mean it doesn't "Fog". After a while, you will notice "halos" around light sources (headlights, street lights, etc). The water is still on the shield, it's just being kept from turning into droplets, so everything gets a bit hazy, but you can still see out of your helmet (a definite plus).
Right, sorry for the book, but there are quite a few factors here to consider. If you don't plan on riding in ultra cold weather, you can forget about the "secondary's", and focus on just the Foggy, is should get you what you need..
