The Smith No-Fog Cloth is some special piece of material. Not only for smith goggles but any eyewear that you don't want to fog up in use. Smith designed it originally to wipe glasses with when wearing them under goggles to stop the fog but can be used on any eyewear or even rifle scopes etc. So not only for snowsports then for anything.
The included instructions say:
For maximum protection use the Smith N-Fog Cloth daily before using eyewear. Ideal for year round use on all types of eyewear, binoculars, rifle scopes and mirrors. For best results breathe lightly on the lens surface, then gently wipe dry with the No -Fog Cloth. Always use on eyeglasses if they are being worn inside a goggle.