Two general categories of kayak helmets exist: full cut and half cut helmets. The difference between the two styles is the amount of coverage: full cut kayak helmets extend low and cover the ears, while half cut helmets do not extend low over the ears and instead end above the ears. The choice between the two is largely a matter of preference. Full cut helmets will protect more of the head, but half cut helmets tend to be more comfortable and looser fitting. Both are acceptable choices for kayaking, though whitewater kayakers may want to consider a full cut helmet for extra protection.
The shell is the outer layer of the helmet. Kayak helmets can feature shells made from a variety of materials, including plastic, Kevlar®, and carbon fiber. In the past, most kayak helmets featured plastic outer shells, and while these were effective in protecting the head, they were prone to shattering upon impact. Modern helmets may still feature plastic shells, but Kevlar® and carbon fiber shells are usually lighter weight and able to resist shattering upon impact more so than plastic can. The downside to these high end materials is the price: both carbon fiber and Kevlar® are likely to drive up the price of the helmet.
An important consideration when choosing among kayak helmets is the strap system. This system keeps the helmet affixed snugly to the head so the helmet does not move or fall off during use. It is important to try on the helmet before purchasing it to ensure the strap system is easy to use and durable. Many modern helmets feature an adjustable fit system that will allow the kayaker to adjust the snugness of the helmet to his or her desired comfort level. The helmet should fit snugly enough that it does not move excessively when the kayaker shakes his head vigorously.
Extreme whitewater kayakers may choose to use full face kayak helmets. These helmets feature an extension that wraps around the front of the face to protect the mouth and nose from impact. These helmets can be clunkier and heavier than other types of helmets, so to combat the weight, many of these helmets are made of lightweight carbon fiber. They are therefore more expensive than other helmet models. A full face helmet is a good choice for a kayaker who will be navigating extremely treacherous rivers with plenty of dangerous obstacles.