Better and cheaper option is to grab some of the lens wipes that most manufacturing plants use. They have an anti-fog solution. Probably a lot cheaper than anything available at a sporting goods store, 100 wipes for less than $10. I usually grab a few from the dispenser before opening day and wipe down all my scopes and binos.
Most of my rifle scopes wear the butler creek flip up covers. If its nice out, no big deal, flip em up and leave em up and hunt all day. But on cold rainy days when scopes may fog, I leave them closed and pop them open only when I need to shoot. Keeps the water off the glass and ensures condensation doesn't form.
Thanks for the info , fellas . I found an article about using a drop of Pert Plus shampoo on a lense . I put a drop on my reading glasses just the one and left the other side without . Placed the pair of glasses over a steaming cup of water and voila - steamed up instantly on the untreated side and the treated side remained clear ! It is supposed to last a few weeks . Rub the solution over the lenses , wait until they are completely dry then buff out with a soft cloth .
exterior fogging is a result of rapid temerature variance. It is actually miniscule water droplets that gave formed an all the surfaces just most visible on the glass when u look thru it. if possible have your gun equalized with the temp somehow before going afield. keep it in your trunk in a case, on the porch or shed if secure, ect........ If the gun is cold when u bring it into the warm the same thing will happen