A thin film of soap does help to keep glasses fog
free. You can mark you glasses with a small piece of
bar soap and then spread the mark out over the lens.
One problem with soap type chemicals on your glasses:
If you put on goggles, similarly treated, it can
be too much soap in the air around your eyes and they
will begin to water. This happened to me on a very
bright sunny day at 12,000 ft, so maybe it would not
happen at all in a more cloudy environment.
Never the less, I have been very careful about spreading
chemicals on my lenses, though I still do it.
Glycerin might work better, but I have not tied it, for
example:
http://www.vitasprings.com/glycerin-glycerine-nature-s-answer.htmlWhat environment are you concerned about?
I have used the more squared-off generic looking cheapo
design goggles that allow any glasses under them.
Some goggles can be very expensive because ski or fashion.
You may have to go to a ski or mountain climbing forum
to get more info on these products.