The helmet is one of the most important pieces of safety gear for whitewater paddling. All kayakers should wear theirs whenever boating - period! In some ways, today's helmets are nowhere as safe as our older style helmets and that is truly unfortunate. Decades ago when I started boating, most manufacturers stocked multiple sizes instead of what many do today, one size fits all. They typically expect each boater to add lots of carefully placed shims to customize the fit. Unfortunately, most outfitters fail to tell their customers and the helmet rocks back and forth on their head usually exposing the forehead - pretty dangerous. Many manufacturers also use a brick hard inner liner that hardly compresses on impact. The stiff liner does a great job of transferring all of the energy from a hit directly to your neck - just what you don't need. Fortunately, there are a few vendors that still produce decent helmets that lack these significant safety issues.
The helmet is one piece of gear you really should purchase locally at a full service boat shop. You can determine if they are full service by asking if they will help you properly adjust the helmet - before you leave the store. I like to test helmets via 2 tests:
- The rock back test - Take two fingers and gently lift at the brow. If the helmet rocks back more than 1/2" - you need further adjustment.
- The smack test - Smack the top of your helmet with a moderate slap. If you feel the full impact, you need more soft padding.
I also recommend trying to wobble side to side but this is less critical than the first two tests.
Many manufacturers have various fancy knobs and other adjustments that come with their helmets to limit rock back. You will need to consult your helmet owner's manual to find the instructions. To get a snug fit, you typically need to add adhesive backed shims in strategic locations. Some manufacturers provide replaceable shells of different sizes (thicknesses actually). You typically find the next size smaller and then shave/sand out foam until it fits snug and comfortable. Shimming on the sides will also prevent wobbling. You also need to be careful not to make it too tight or you will get a splitting headache and be inclined to paddle without the helmet - bad move. Helmet fitting takes time unfortunately and must be done before you head out to the river.
Another useful helmet addition is a brow if one already isn't incorporated. These not only help shade your eyes but they can divert water from your face if trapped in a falls so you can more easily breath. Some brands also have add-on ear pads but I would rather wear a full coverage helmet rather than the common baseball cap style prevalent these days.
To recap the most important helmet attribute is a proper fit and that is why we need to customize as one size really doesn't fit all.