A while back I called Leupold technical supportand asked them the very same question because I hunt in very humid environments and had problems with my binocular lenses fogging up (on the outside)when I looked through them. They recommended a product called kleer-vu. It is an anti-fogging compound that won't harm the multi-coatings on optics. I have been using it for three years on all of my optics. Works great, but you have to re-apply it monthly for optimum performance. Order the small bottle....it will last you for years.