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Summary: Helmet users sometimes are annoyed that it seems they need a different helmet for every sport. In many cases you do, but in a few others you can find a multipurpose helmet.
Some sports have unique problems. Equestrian helmets have to withstand the sharp edge of a horse's hoof. Whitewater helmets have to deal with "bucketing" in very fast water flows and drain well. Hockey helmets need facial protection. Football helmets are designed for thousands of blows per season. Auto racing helmets must be fire-resistant. The list goes on, and you can probably add an example from personal experience.
In some sports, crashes are not frequent and the helmet can be discarded when a big impact occurs. Others involve
constant falling and many many smaller impacts. For these sports a one-use helmet would be a nuisance, and probably would
not be replaced when it should be. So some compromises are normally made in protection to make the helmet
multi-impact.
Single use helmets are mostly made with expanded polystyrene (EPS) because it is cheap, light, easy to manufacture and has excellent crush characteristics with very little rebound. Once crushed it recovers some part of its thickness, but does not recover its protection. If you don't discard it after the first hit, you will be in for a nasty surprise if you happen to hit on the same spot for a second hard impact! Bicycle, motorcycle, roller skate and equestrian helmets normally use EPS for impact energy management.
The first multi-use bicycle helmets were made with expanded polypropylene (EPP). EPP looks like EPS, but has a slightly rubbery feel. It recovers slowly after a blow and is good for more hits. Nobody can tell you how many more hits, but some. Its crush and manufacturing characteristics are not quite as good as EPS, so the helmet might have to be thicker, and it rebounds enough during the impact sequence to make it less than ideal, although the rebound occurs after the lab has measured the performance of the helmet and is missed in standards testing. EPP is used extensively in automotive padding, for things like the foam to back up a bumper. There are now on the market a few EPP helmets that meet both the CPSC bicycle helmet standard and the ASTM F1492 skateboard helmet standard. They have stickers inside telling you that. We list them on our page on dual-certified helmets.
Multi-hit helmets are mostly made with butyl nitrate foam, a "squishy" but dense foam that is good for many impacts. It is mostly black or gray. It is heavier than EPS and cannot manage as much impact energy for a given thickness. Hockey and football helmets are made this way, and so are whitewater, old-style skateboard and aggressive trick skating helmets. You don't have to throw the helmet away after a hit, but it normally is not much thicker than an EPS helmet, and that means it will not manage as big an impact. Typical lab drops for multi-use helmets are one meter. For single-use EPS helmets the typical drop is two meters. That's a very large difference in impact protection.
Another "squishy" foam, but with superior impact characteristics is the foam marketed by W Helmets as Zorbium. Behind
the glitzy name is a really good foam, good for multi hits and "rate-sensitive" to make it stiffen up if the impact is
really hard and ease up if the impact is lesser. It might be a good choice if avoiding concussions is your primary goal.
(Most helmets are designed to protect primarily against the high-end impacts that cause catastrophic brain injury,
letting enough energy through to give you mild concussions.) Zorbium helmets from W Helmets are hot, heavy and soak up
sweat, but some of them meet bike, ski and skateboard standards.
The Snell Memorial Foundation had a multi-purpose standard, called Snell N-94. Snell
believes that based on their testing of those helmets they offered adequate protection for "non-motorized activities" but
their description of the standard limited that to bicycling, roller skating and skateboarding. The standard was not used
by manufacturers and has now been withdrawn.
The amount of protection you are willing to settle for is, of course, your own personal decision in areas that don't have helmet laws. If you wear a skateboard helmet for bicycle riding that does not have the CPSC bicycle standard sticker inside you might think it's better than nothing, but you should know that a significant percentage of the head impacts will be more than that helmet can take and keep your brain in one piece. When a CPSC helmet is only about $20 at a discount store, and Consumer Reports is finding that cheaper helmets are more protective anyway, why risk it? Or if you send your child out in a bike helmet to do some halfpipe skating or snowboarding where falls are constant, you will have no way of knowing when the child returns whether that helmet they will wear again next time had an impact that ruined it or not. The child will not know, since helmets cushion the blow, or will just forget to tell you. Although this advice is annoying, a different helmet may be the only way to have maximum protection. Helmets don't work every time anyway, and compromising by using a helmet not designed for the activity is stacking the deck against the user.
If you run across any true multi-purpose helmets that we don't know about in our annual writeup or our dual certified helmet page, please drop us an email!