A helmet is a helmet, right? With a quick glance at a helmet display they can all look the same, but there are some big differences between a $25 and a $250 helmet.
Let's start with testing. Here in the United States there's only one test that matters: the Consumer Product and Safety Commission, or CPSC, test. This is the organization that is in charge of safety testing (and recalls) for most of the products you use in your home. There are other organizations out there that test helmets independently, but without a CPSC passing test you won't be able to sell the helmet for bicycle use in the United States. This test is no slouch either--there have been notable cases of helmets that were popular in Europe unable to be sold in the States due to not meeting CPSC standards.
So, what are they actually testing in this process? They test eight helmets of each size available. Two are tested after being at room temperature, two are exposed to freezing temperature, two are subjected to over one hundred degree conditions, and two are submerged under water. After 24 hours of exposure to these various environmental conditions they are tested in four areas of safety:
First up is vision. The rider requires 210 degrees of vision while the helmet is on. This is simply tested by panning a camera placed inside the helmet.
After the vision test the chin straps are tested for stretch. In this test, a 4 kg weight is attached to the chin straps and allowed to drop .6 meters. The amount of stretch in the straps is recorded. Measured stretch during this test must be less than the amount viewed as potentially causing the helmet to come off in a crash.
The last two tests are impact standards. In the impact test, a "headform" that is just barely big enough to be secured inside the helmet is equipped with a weight to simulate a riders head. The helmet is then dropped from a height of 6 feet into various shaped anvils. First of all the helmet must stay on the "headform" in this simulated crash. Secondly, it must also reduce the impact of the "headform" to a prescribed amount.
If the sample group of helmets tested all pass these four test categories, vision, stretch, retention, and impact reduction, then the helmet is approved for sale. There is no A+ or C- grade, all helmets must pass every category.
So, if every helmet passes the CPSC test, what differentiates your basic helmet from your flagship model? The three key characteristics are comfort, ventilation, and weight. Lets go through a basic run down of the helmets and examine the features.
From the exterior, these helmets looks pretty similar. However, comparing the basic helmets on the left to the progressively more featured helmets going to the right, you'll see an increase in the cooling vents molded in the shells. The apparent exterior ventilation differences are not the end of the story, however.
Let's take your basic helmet, the Avenir Avenue. While there are ventilation holes on the helmet itself, these holes dead end at your noggin. This design does not allow for much air flow along your head. The padding on the inside of the helmet is adequate, but not extensive. There is a small pad that goes across your forehead, and a small pad on the top of your scalp. Replacement parts are not available for this helmet.
Next up is the Bontrager Solstice. Notice the substantial padding on the interior. Also, the front ventilation holes are connected to the rear ones by a small channel running over your scalp. This allows some of the air to flow in from the front of the helmet, over your scalp, then exit further back. The cooling effect is noticeable. In addition to the increased ventilation the padding and fit dial are easily replaceable parts.
Further down the line is the Bontrager Circuit. This fine specimen of safe riding gear ups the ante from basic to enthusiast level. Aside from a much sleeker, polished exterior the ventilation is a big step up. The interior ventilation channels are interconnected, running from front to back and connecting from left to right in addition to being deeper than previously seen. Not only is this good on hot days, but this keeps your head dryer in cool conditions. Few things can cause the loss of heat faster than a wet head on a cold day!
Next up is the Giro Atmos. This has been a perennial favorite helmet from the avid rider to the pro racer. This helmet has extremely deep channels, giving it a nearly transparent look and feel. This is a helmet that is easy to forget is on your head. The carefully controlled ventilation system provides unparalleled comfort without any compromise to safety. This is the standard for "barely there"
But what about those rounded helmets you may ask? Those are what are referred to as a "skate" or "bmx" style helmet. These generally provide almost no ventilation, but are rated to a higher standard called ASTM F1492 certification. The big difference is these helmets are tested for multiple impacts. Your standard bicycle helmets are rated for a single impact followed by mandatory replacement. The skate style helmets are designed and tested to be able to take multiple reasonable impacts. However, one should always carefully inspect their helmet and at any sign of damage, replace it.