When I'm cross-country skiing, I usually wear glacier glasses to protect from the intense glare off the snow. When I'm moving, they usually stay clear . Whenever I stop though, my glasses seem to fog up almost instantaneously. It's a pain to have to wipe them off, and takes a while for them to clear back up when I get going again. Is there anything I can do to prevent my glasses from getting fogged up?
Ventilation is your friend.
I hate to say it - but the glasses I've found that have this dialed are usually a little more expensive. After suffering through fog, wind sheer, and poor optics, I found a high end pair of glasses in the back-country, and my eyes were opened.
As a second option, removing your glasses immediately when you stop (or even sliding them to the end of your nose) might keep the the steam from your face and breath from clouding them up for a few moments longer.
As a third option, saliva is an old scuba-diver trick to keep masks from fogging up. Spit on your lenses that wipe them clean. (I've had limited success in non-aqueous environs.)
A small travel-size shaving foam (not gel), is an inexpensive alternative to relatively pricey anti-fogging treatments. Single towels can be found in car wash vending machines for about $1.
Apply small amount of foam inside and outside of lens. Using a soft, lint-free towel and using a circular motion, fully cover all exposed lens area with foam and then wipe clean. Do not touch the lens with your fingers. Skin oil will breakdown protection.
You can carry these items with you for reapplication when necessary. I cut the towel in half, and tuck the foam and towel into an inside pocket of my jacket.