The Hidden Expiration Date on Your Bike Helmet: Safety Experts Explain Why
In an era of rising costs and conscientious consumption, many of us adopt a "save for a rainy day" mentality. We cherish leftovers, embrace recycling, and find value in well-worn items. Yet, this practical mindset requires vigilance: expired products, from medicines to cosmetics, must be discarded. Surprisingly, this list includes bike helmets—a critical piece of safety gear without a stamped expiration date.
Why Bike Helmets Have a Lifespan
According to the Consumer Product Safety Commission and the bike industry, helmets should be replaced every three to five years. More urgently, they must be swapped immediately after any fall or crash where the head contacts a hard surface, even if no injury or visible damage occurs. With premium helmets costing over $300, riders often question this guideline. What materials warrant such a timeline, and who established this rule?
First, always wear a helmet: Studies show they reduce brain and head injury risks by 63% to 88%. All helmets sold meet ASTM International safety standards, as noted by Tucker White, global bike category manager at SMITH, a sports gear manufacturer with six decades of experience.
Inside Your Helmet: Materials That Matter
Helmets share a basic structure: a polycarbonate outer shell and a comfort liner, with key protective layers in between.
- EPS (Expanded Polystyrene) Foam: The foundational safety material, known for being moldable, lightweight, and highly shock-absorbent. "It's also used in coolers and packaging," said Graham Sours, commercial director at KOROYD.
- KOROYD: An impact layer of thermally welded polymer tubes that crumple on impact, mimicking vehicle crumple zones. It's placed in common impact areas—sides for mountain biking, back and top for road cycling.
- MIPS: A slip layer that reduces rotational forces during angled impacts, allowing the helmet shell to move independently from the head.
- WaveCell (Trek Helmets): A proprietary honeycomb material that expands when stretched and flattens when compressed, focusing on rotational impact protection.
The Science Behind the 3-5 Year Rule
Research from 2016 and 2017, cited by Barry Miller of the Virginia Tech Helmet Lab, found that EPS foam in helmets up to 26 years old showed no significant degradation. However, other components may deteriorate. "As a brand, we approach protection with abundance of caution," White emphasized, noting unpredictable consumer use.
Sours compared EPS to a sponge: left exposed, it dries out, becomes brittle, and breaks. Factors like frequent drops, sun exposure, and even sunscreen sprays can accelerate wear. Michael Bottlang, a researcher, added that sunscreen chemicals can degrade plastics, making precise timelines challenging.
For helmets stored in controlled environments and rarely used, White suggests a maximum lifespan of 10 years from manufacture. Crucially, all safety materials are single-impact: any head strike necessitates replacement. "Impact loads from moderate-speed falls reach thousands of Newtons—far higher than expected," Bottlang warned.
Why Replacement Matters Beyond Crashes
The bike industry continuously innovates with new technologies and materials, offering another reason to upgrade. Whether you're a mountain biker, road cyclist, or casual rider, protecting your head is paramount. When viewed as safeguarding your most vital asset—your brain—the cost of a new helmet pales in comparison to the risk. In matters of safety, it's always better to err on the side of caution.
