Helmets protect in different ways depending on the shape, style, or model. A full face protects the face as well as the rest of the head. The three quarter protects everything the full face does accept for the face. A half shell covers only the top and back of the head.

The hard surface of the helmet varies in composition from brand to brand. Generally, it should rest impact, small rocks, and other small objects. Older designs use a crumple zone type technology. This works by the shell compressing into the interior and the foam interior protecting the head from impact. The downside is this is only works for one good collision. (One hit) D.O.T. rated helmets require this type of function. Higher end or newer helmets are made from carbon fiber and or kevlar which are protective for multiple or possibly unlimited impacts.

The last layer of protection just before your head is the interior helmet lining. Some are made of cotton or terrcloth. Others are made of some type of memory foam which does a better job of disbursing energy rather than transferring it to you head.

The interior liner is the last layer before impact energy would transfer to the head. Some liners are cloth or cotton. A high quality liner would consist of memory foam which does a remarkable job for disbursing energy instead of transferring it into the rider's head.

Some helmets are DOT rated, other carry a different rating such as SNELL. Some helmets to not have any particular rating. Aside from legal obligations, the quality and material makeup of the helmet is far more important that the rating sticker. DOT helmets are made for one hard impact. Once the helmet has compressed or damaged, it needs to be replaced. Helmets constructed with carbon fiber or kevlar are protective for several impacts.

The choice of helmet you wear is ultimately up to you. There may be outside factors that influence your decision such as local laws or rules. Just remember that it's your head and no one is going to look out for your own safety like yourself.