Wow! I’m officially impressed! This is one well-designed product. Alpinestars’ Thermal Balaclava will be a favorite when facing the harshest of winter temperatures. The head part is made of a thin stretchy nylon that shouldn’t effect helmet sizing significantly. There is an eye opening and a cutout for the nose and mouth. You can also tuck the nose/mouth part under your chin if it’s not that cold. Below the head part there is a two-part skirt. The first part is a soft fleece material that would go under your jacket to seal out drafts and to insulate, then the outer skirt is a stretchy, but waterproof material that will block wind and rain to keep it out of the jacket collar. There is also an adjustable cord to tighten the outer skirt around the neck. Happy riding in cold weather with this thing!