Wore this today with my thick balaclava and ski goggles.
Al Fullface Helmet from Pryme..980gm of hand laminated fiberglass. ran around 100 bones though they might be cheaper now.
You do not want to ride this in the summer unless you are doing something seriously fun...read: potentially dangerous.
Pro DH helmets I believe are more robust crash wise..and tend to lean towards carbon fiber
I've never had to cover the vent holes and for the most part never had to wear anything underneath to keep the head warm unless it's frigid out. (-15C and lower)