Bike Helmets Expire. Here’s When You Should Replace Yours.

As an increasingly reluctant consumer, I try to get the most out of my money. I eat leftovers, believe in recycling and repurposing, and appreciate the beauty of a well-loved, worn upholstered chair. I’m a “save for a rainy day,” “just in case,” and “you never know when you might need that,” kind of person.

In a world where the price of goods keeps rising, I suspect I am not alone. This sort of mild hoarding, though, means I (we) need to remember to occasionally check for and throw out expired products: things like medicines, cosmetics, sunscreen, smoke detectors (among others) and ― shockingly ― bike helmets.

While you’re not going to find a specific date stamped on the inside of your helmet, the Consumer Product Safety Commission and the bike industry state that you should replace your helmet every three to five years or ― and this is arguably the key piece of information ― immediately after a fall or crash which involved your head coming in contact with a hard surface. This advice holds even if you’re not physically injured (yay, your helmet did its job!) and even if there is no apparent damage to the helmet.

With some bike helmets priced in the $300+ range, you may be wondering if replacement is necessary if you haven’t been involved in a crash, who came up with this rule, and what are bike helmets made out of that they have expiration dates? We talked to the experts to find out.

First, yes, you should always wear a bike helmet: They provide a 63% to 88% risk reduction for brain and head injuries.

Second, all helmets must pass the same ASTM International safety standards and adhere to the same parameters to be sold in their intended market, said Tucker White, the global bike category manager at SMITH, a company that has been manufacturing sports gear for 60 years.

While each helmet is individually designed, they all start with a polycarbonate outer layer, or plastic shell, and end with a performance comfort liner. In between these, you’ll find one of, or a combination, of the following:

• EPS (expanded polystyrene) Foam: The OG of bike helmet safety, moldable, lightweight, rigid and extremely shock absorbent. “You also find it in many different commodities like coolers and packaging,” said Graham Sours, commercial director at KOROYD.
• KOROYD: An impact protection layer made of a series of “thermally welded polymer tubes” designed to crumble instantly on impact, employing the same idea that car manufacturers use with ’crumple zones’ in vehicles. “We put KOROYD in specific locations that research shows are the most common impact locations,” explained Sours. For mountain biking, this means the side of the head, while road cycling, the back and top.
• MIPS: brain protection layer for rotational impact (when your head hits a surface on an angle). “MIPS creates a slip layer between the head and helmet, allowing the helmet shell to rotate independently from it, rather than transferring those rotational forces directly into the head,” explained White.
• WaveCell and Trek Helmets: a proprietary material found only in Bontrager/Trek bike helmets. Like MIPS liners, WaveCell focuses on head injuries from rotational impact. Constructed with a honeycomb structure, WaveCell possesses a “bendy” feature, like bendy drinking straws do, which allows it to expand when stretched, and flatten when compressed, the opposite of how most things behave.

Back to the expiration question: How do these materials behave and do they change over time? How did the industry and experts settle on the three to five year recommendation for any helmet whether it has been in a crash or not?

Barry Miller, director of outreach and business development at the Virginia Tech Helmet Lab, pointed to research studies published in 2016 and 2017 that showed the EPS in helmets up to 26 years of age did not suffer any degradation, with the caveat that there are certainly other bits and parts of a helmet that could.

“While studies have shown there is not significant degradation of EPS and other materials over time, as a brand, it is important to approach protection products with an abundance of caution since we don’t know how consumers are using and treating their gear,” White said.

Sours explained that how many times you throw your helmet into the back of a car and/or drop it, and the amount of sun exposure it’s subjected to, contribute to its longevity.

All the industry experts we spoke to said that while it’s certainly true that brands issue their replacement guidelines from a partially legal standpoint, none would recommend completely ignoring it.

“Think of EPS like a sponge,” Sours said. “If you leave a sponge in your sink, over time it will dry out, get brittle and break apart.”

Bottlang added that some sunscreen sprays can also be harsh to plastics, causing it to break down over time, which is why it’s difficult for any brand or researcher to give a hard timeline.

If you want to assign a more specific expiration date to your bike helmet, White said that if you, say, bought a helmet but never or rarely wore it and you stored it in a temperature and humidity-controlled environment, the replacement recommendation would be no longer than 10 years from the manufacturing date.

Remember (because it’s definitely worth mentioning again), all bike helmet safety materials are single-impact use. Hit your head once, and it’s time to replace your helmet.

“Impact loads when you fall from a bike, even at moderate speeds, are in the thousands of Newtons,” said Bottlang. “Way higher than you think.”

The bike industry and gear industry in general continue to research and create new technologies and advancements in materials which, as Miller pointed out, provides a great reason for replacing your helmet.

The great thing is you don’t necessarily have to be a mountain biker or an avid road cyclist to benefit from these technologies and materials to protect the most precious and necessary part of what makes you you. And, when you think about it like that, why would you take the chance that your helmet won’t do its job? When it comes to my head and brain, for my money (and peace of mind), it’s always better to be safe than sorry.