It isn't the water molecules passing through the mask from your mouth. Your body is warmer than the air around you most of the year (unless you live in the trop

It isn't the water molecules passing through the mask from your mouth. Your body is warmer than the air around you most of the year (unless you live in the tropics). It is mostly the heat of your breath passing through the mask, then hitting the cooler surface of the glasses, and making the moisture in the air that is already outside your mask condense on the glasses.