Braincaps & Half Shell Helmets Skullcap or half-shell helmets offer the best ventilation of all. So they are ideal for short trips in hot weather. When buying a skullcap helmet, comfort and appearance are usually the key considerations. By the nature of the design, you do not get the same degree of protection as with other types of helmet. If you're in any doubt, you can order two different sizes from Louis online and try them out. Louis will take back any item that does not fit or which you do not like.