Surf helmets tend to be used by extremists, the ultra safety-cautious, and GoPro® HD Cameras POV filmers. I’ve used the helmet pictured (Gath Gedi) to attach a mount for a GoPro video camera.
Through trial and error, including three broken surfboards in one session, I found that I had to be riding the barrel so deep (behind the shock wave and on the foam ball) to get a decent head-cam barrel clip that I eventually gave up on it and no longer use the helmet for surfing.
Gath is the most popular helmet used for surfing, but they are also commonly used by wind- and kite-surfers, kayakers, bodyboarders, stand-up paddle boarders, and even skiers, snowboarders, and skydivers.
Gath helmets are extremely light and have comfortable inserts that can be added for a perfect fit, which fit inside of the rigid plastic shell. Gath helmets come in a wide variety of styles and colors, including the Original Surf Helmets, which are the most basic design, and the thick Water Communications Helmet, designed with a headset used to communicate via radio.
Some guys like the Gath helmets with the tinted-plastic face shield, but I don’t really like the shield because it restricts vision. My favorite Gath helmet is the Gedi, because it’s the smallest model and has removable ear pieces.
Some negative feedback about Gath helmets is that they scoop water when duck-diving, which drains irritatingly down the eyes and face for a few seconds after surfacing from each wave.
The positive feedback about Gath helmets is that they are lightweight, affordable, and can save your life.
Some friends who surf giant waves make their own helmets by taking a mold of their head and wrapping it in Kevlar with resin. They do this because Kevlar is much more durable than the plastic Gath uses.
If you want a helmet for use in the aquatic environment, I recommend going with Gath.
Video: John Maher using the Gath Gedi to get POV clips with a GoPro camera.