I saw an ad in one of the mass market motorcycle magazines for Cat Crap. Cat Crap is a gelatin-like substance you are supposed to smear over the inside of your goggles/glasses/faceshield to inhibit the formation of fog.
Cat Crap has been marketed to skiers for decades. Now that it's being marketed to riders, I recommend you not use the product until you are ABSOLUTELY SURE the product is safe for application to the material.
I learned the hard way what Cat Crap can do to the proprietary coatings on protective eyewear when it dissolved the coating on an expensive polarized Oakley ski goggle lens. Luckily both had been purchased at REI, so my lens was replaced at no cost, but it just might do the same thing to the expensive coatings on your sunglasses, goggles, or faceshield.