What is a Low Density Layer and Why Your Next Helmet Should Have One

LDL—short for Low Density Layer—is nothing new in helmets. In fact, Kali has been designing helmets with low-density materials for decades, even though they aren’t required to pass current helmet certification tests. Why?

Simply put, we believe that incorporating lower-density materials next to your head is one of the most critical elements in reducing injury during real-world cycling crashes. Even more important than the well-known MIPS system.

Certification Alone Is Not Enough
Certification tests for cycling helmets typically allow up to 200 g’s of impact energy transmitted to the brain. That’s a big hit, which requires a relatively hard (i.e., high-density) helmet to manage. But real-world crashes don’t always look like certification lab tests.

According to research by Dr. Mazdak Ghajari at the Imperial College London, there’s a 25% chance of mild traumatic brain injury (MTBI) at just 66 g’s, and an 80% chance at 106 g’s. Those aren’t impacts that would fail a certification test—but they’re well within the range of forces that riders experience in everyday crashes. Unfortunately, most standard EPS foam doesn’t begin to meaningfully compress until forces are much higher.

Here’s Where LDL Comes In
EPS foam is a very versatile material, but the nature of helmet certification tests means most EPS we see in helmet designs are of a density intended to manage high-energy impacts, but it doesn’t start dissipating energy until the force reaches a relatively high threshold. In contrast, low-density materials used in LDLs begin to compress and absorb energy immediately—at much lower forces.

By adding softer, low-density materials to a helmet, we expand its dynamic range—its ability to respond to both high- and low-energy impacts. The dense foam helps protect in severe crashes. The LDL helps manage the more frequent, lower-force impacts that still pose a serious risk of concussion.

It’s not the cheapest or flashiest way to build a helmet—but after Kali’s decades of engineering, testing, and validation, we’re confident that putting something softer next to your head is one of the best ways to reduce your risk of injury.

What Is the LDL, Exactly?
It varies depending on the helmet model, but in general, Kali incorporates LDL in one of three ways:

●       An added layer of softer EPS foam (which must generally increase overall helmet thickness)

●       Conehead™ technology, which uses dual-density EPS formed into energy-dispersing cones, often with Contigo™ material for superior impact control (typically used in full-face helmets)

●       Non-EPS energy management layers—specifically ERT™, a patented soft polymer grid that can be integrated into any helmet

In all three cases, the goal is the same: increase the helmet’s ability to absorb energy at lower forces by putting a softer material next to your head. ERT™ is a powerful tool in this system, but it’s part of a broader commitment to using lower-density materials wherever they are most effective. Internal testing—even on helmets that didn’t initially perform well—has shown significant improvements when more ERT™ is added.

What About MIPS and Rotational Impact Energy?

Fun fact: Kali does not offer a single helmet with MIPS. While we agree that managing rotational impact is critical, we don’t believe that MIPS—a hard plastic slip layer placed next to your head—is the best way to do it. Does MIPS help reduce rotational energy? Yes. Is it the best way to also manage the more common sub-200g linear impacts that we believe matter most? We don’t think so. We think an LDL is significantly better.

How Kali Manages Rotational Energy Without MIPS

The MIPS system addresses rotational impact by creating a slip plane, allowing the helmet to move slightly on your head to absorb rotational energy. Kali takes a different approach: our LDL systems are inherently soft and low-density, which allows them to compress both linearly and laterally—managing rotational forces without adding a hard plastic liner.

Independent lab tests show that our LDL-equipped helmets manage rotational impacts as well as, and often better than, MIPS-equipped helmets.

Kali Was First to Bring LDLs to Market

Anti-rotational and low-G impact protection is no longer new to riders. From weekend warriors to world-class racers, you’ll see plenty of helmets sporting those yellow MIPS stickers. But that little dot often gives riders a false sense of security—many wear it without fully understanding how it works or how effective it really is.

At Kali Protectives, we believe we helped start the conversation around anti-rotational and low-G impact protection. And while we’re not usually the type to say, “We did it first,”… well, we did.

Our original Bumper Fit system laid the foundation for what we now call our Low Density Layer. First introduced in our Phenom, Maraka, and Loka road helmets back in 2012, Bumper Fit was a specially formulated memory foam designed to reduce both impact energy and pressure points. It helped distribute force more evenly across the head, improving comfort while enhancing protection.

From the beginning, we knew helmet design had to go beyond sleek styling and flashy graphics. We set out with a clear mission: to raise the bar on what riders should expect from their helmet.

And like most things worth doing, innovation takes time. With every new generation of LDL—whether it’s RHEON, yellow QuadCore, or our latest blue ERT™—we’ve continued investing in research, refining our materials and technology to stay at the forefront of head protection.

So while we’re hard at work in the lab, you can focus on what matters: riding.

We’ve got your head covered.

Find your LDL equipped helmet today!