One of the best parts of owning a bicycle is shopping for all the gear and accessories that you need to go along with it, from bike lights to stay visible on the streets to bike locks to keep it safe when you’re at the shop. But no piece of equipment is more important than a bike helmet.

But does buying a more expensive helmet mean you get more protection? What features do you need for what you intend to do, and how often do you have to replace it? And what the heck does MIPS mean? Let me walk you through the jargon and help you make sure your brain stays safe in your skull.

What Type of Helmet Do I Need?

That depends on the kind of riding you do. If you just ride 1 to 5 miles on city streets to work, a commuter or everyday helmet is fine. Some have more or less ventilation or look more or less cool. Others, like the Thousand Chapter MIPS ($145), have commuter-friendly features, like a punch-out hole that lets you lock up your helmet with your bike.

If you’re a road cyclist, you need a road helmet like the Kask Utopia Y ($300), which takes aerodynamics, ventilation, and weight into account. A road helmet has to help you go against the wind, keep sweat from dripping into your eyes, and be comfortable for long hours of riding. Mountain biking helmets like the Smith Forefront 2 ($270) cover the back of the skull and often have a visor, and sometimes even include clips to fasten eye protection or googles.

How to Fit Your Helmet

The best way to buy a helmet is also the best way to buy a bike: Try it on. Most helmets today come with a dial system at the rear of the helmet, allowing the rider to adjust their helmets for a more precise fit than ever before. The adage goes “low, level, snug”: Your helmet should sit level on your head and cover almost all of your forehead.

A good rule of thumb is that your index finger should fit in the space between your eyebrows and your helmet. Anything more and the helmet isn’t sitting on your head properly. The strap should be snug enough beneath your chin that you shouldn’t be able to easily fit a finger between your jaw and the strap. You should also not be able to move the helmet more than an inch or so in any direction.

What Is Mips?

If you’ve bought a new bike helmet any time in the last few years, you’ve no doubt noticed a tiny yellow logo with the word “Mips” printed on it somewhere on the helmet’s shell. Mips is an acronym that stands for “Multi-directional Impact Protection System.” It’s an in-helmet system that reduces the rotational impact that is common during most crashes.

An inner webbing—what the brand calls its “low-friction layer”—fits snug to your head. This webbing is connected to the helmet’s outer shell with a series of fasteners. The low-friction layer and the helmet’s outer shell are able to move independently of one another. If you crash while wearing a Mips helmet, the mobility of the low-friction layer works to redirect the rotational forces of impact away from the head.

Mips was developed in the mid-1990s, when Swedish brain surgeon Hans von Holst realized that contemporary helmets weren’t doing enough to protect against brain damage. Von Holst noticed that helmets were designed and tested for impacts at straight angles. However, cyclists very rarely have head-on impacts from a crash. Von Holst and his team began to test impacts from a variety of angles to develop a system that could rotate within the helmet, thereby diffusing the force of impact from the head.

After more than a decade of study and design, Mips launched its first product, a proprietary helmet, in 2007. Soon after, Mips became what’s known as an “ingredient brand,” selling its technology to megabrands such as Giro, Smith, and Specialized. Hence, the now-ubiquitous little yellow logo.

Are There Other Safety Systems?

While Mips is easily the most popular rotational impact system and arguably the industry standard, it’s not the only one. Several companies have developed their own proprietary systems that essentially perform the same function as Mips.

For example, the motocross brand 100% outfits most of its new helmets with its proprietary Smartshock system, where a series of tiny elastomers allow the helmets’ inner webbing to move independently of its outer shell while absorbing the forces of impact. According to 100%, Smartshock is effective across a wide range of speed and impact types.

Giro, one of the most popular helmet brands on Earth, recently released its new Spherical technology, which is a ball-and-socket system that allows an upper shell to rotate on top of a lower shell in order to redirect impact forces away from the head. (It’s worth noting here, though, that the Giro Aries Spherical Helmet ($250) still has a Mips system.)

Trek, another of the world’s biggest brands, rolled out its WaveCel system a few years ago. Essentially a crumple zone built into the helmet, WaveCel is a thick, firm inner layer that can flex to reduce initial impact, crumple to absorb energy on impact, and glide to, like Mips, redirect energy from the head. Finally, similar to Trek’s WaveCel technology, the Koroyd system uses a series of tubes which crumple instantly and consistently on impact, absorbing the maximum force sustained during a crash. Some helmets, such as the Smith Persist ($130), meld both Mips and Koroyd systems beneath a single shell to offer an added layer of protection.

Do You Need a New Helmet?

Even if you are a year-round rider and you have a helmet you love, the general rule of thumb is that you should retire it after three to five years. UV exposure, salt-laden sweat, and daily use all contribute to the degradation of helmets.

Finally, helmets are not meant to be worn after a crash. Even if the spill is minor and the helmet looks and feels perfectly fine, trash it and get a new one. Some brands even offer crash replacement options. Even if your helmet is trashed, take comfort in knowing that it’s done its job and kept you safe. It deserves a peaceful, sweat-free retirement.

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