MIPS, short for Multi-directional Impact Protection System, is a thin plastic layer inside a helmet that slides 10 to 15 millimeters during an angled impact. That small movement redirects rotational energy away from your brain, reducing the twisting forces most likely to cause a concussion. The technology was developed by Hans von Holst, a brain surgeon at the Karolinska Institute in Stockholm, alongside Peter Halldin, a biomechanics researcher at KTH Royal Institute of Technology.
Why Rotational Force Matters
Most real-world crashes don’t send force straight into the top of your head. You hit the ground at an angle, which means your skull both decelerates and rotates. Traditional helmet foam (EPS) is excellent at absorbing the straight-line energy of an impact, compressing to slow your head down. But it does relatively little about the rotational component.
Rotational force is particularly dangerous because of how your brain sits inside your skull. Your brain is soft, loosely tethered to the skull by blood vessels and thin membranes, and surrounded by fluid. When your skull suddenly rotates and stops, the brain keeps moving, twisting against itself. This creates shear strain, where adjacent layers of tissue slide past each other. The theory dates back to 1943, when researcher A.H.S. Holbourn demonstrated that rotating a skull-shaped cavity could cause large deformations in a gel inside it. Modern imaging confirms this: during angular acceleration, the dominant injury mechanism is radial-circumferential shearing, particularly in deep brain structures like the corpus callosum, the bridge connecting your brain’s two hemispheres.
Concussions, diffuse axonal injury, and other traumatic brain injuries are strongly linked to this rotational shearing. A helmet that only handles linear impact leaves a significant gap in protection.
The Slip-Plane Layer
MIPS addresses rotational force with a deceptively simple concept: a low-friction layer between the helmet’s comfort padding and its energy-absorbing foam liner. This layer is typically a thin sheet of polycarbonate plastic, anchored to the helmet by four small rubber ties. During normal wear, it stays in place. During an angled impact, the rubber ties stretch and the plastic layer slides against the foam, allowing the helmet shell to rotate slightly relative to your head.
That movement, roughly 10 to 15 millimeters in the most common version, mimics what your brain’s own protective fluid does on a smaller scale. By letting the helmet redirect some of the rotational energy over a slightly longer time window, the peak twisting force that reaches your brain drops. Early MIPS designs used a Teflon-coated interface between two concentric shells connected by a breakaway pin. Current versions are simpler: a thin, uncoated polycarbonate sheet with small fabric pads at contact points to reduce friction.
How Much Protection It Adds
A 2021 study published in the Annals of Biomedical Engineering tested bicycle helmets with and without MIPS across multiple angled impact scenarios. The results varied depending on the helmet model and the angle of impact, but the pattern was consistent. MIPS-equipped helmets reduced peak rotational acceleration by 22 to 52% in the majority of test conditions. Brain strain in the corpus callosum, one of the areas most vulnerable to rotational injury, dropped by 17 to 54% depending on the impact angle.
Overall brain strain was significantly lower in 60% of MIPS helmets during two of the three impact scenarios tested, with reductions ranging from 23 to 66%. The results weren’t uniform across every helmet and every angle, which reflects the reality that helmet shell shape, foam density, and fit all interact with the slip-plane layer. MIPS doesn’t transform a poorly designed helmet into a great one, but it consistently improves the rotational performance of helmets it’s added to.
For context, the same study tested other anti-rotation technologies. An airbag-style helmet (the Hövding 3.0, worn around the neck and inflated on impact) reduced brain strain by 82 to 90%, far exceeding any traditional helmet. WaveCel, a collapsible cellular liner, showed meaningful reductions in some impact angles but not others. MIPS fell in between: not the most dramatic improvement available, but the most widely adopted and consistently effective across different helmet designs.
Different MIPS Versions
Not every MIPS helmet uses the same design. The technology comes in several versions tailored to different helmet types.
- MIPS Evolve is the most common version, a refined slip-plane with improved ventilation compatibility and lighter weight than earlier designs.
- MIPS Integra is built directly into the foam liner rather than sitting on top of it. It’s nearly invisible inside the helmet and is one of the lightest options.
- MIPS Air Node is integrated into the comfort padding itself, making it the lightest and most ventilation-friendly version.
- MIPS Spherical was co-developed with Giro and Bell. It uses a ball-and-socket design with two separate foam layers and a slip-plane between them, so the entire inner liner rotates within the outer shell.
- MIPS Elevate is designed specifically for construction hard hats rather than sport helmets.
The core principle is identical across all versions. The differences come down to where the slip-plane sits, how much it affects ventilation, and how seamlessly it integrates with the helmet’s shape.
How It Feels When You Wear It
Early MIPS helmets had a reputation for feeling slightly roomier or less snug, since the plastic liner added a layer between your head and the foam. Current designs have largely eliminated that tradeoff. Versions like Integra and Spherical are engineered to maintain the fit profile of the base helmet, and MIPS variants don’t meaningfully change labeled sizing in current models. You should choose your normal helmet size and adjust with the retention dial as usual.
Weight differences are minimal. The slip-plane layer adds grams, not ounces, and newer versions like Air Node were specifically designed to keep weight as low as possible. Ventilation is similarly preserved in modern helmets. The Spherical and Integra approaches move the slip interface into or between the foam layers, keeping vent channels clear. Whether you notice any difference in airflow depends more on the base helmet’s design than on the MIPS layer itself.
During an actual crash, you won’t feel the MIPS layer activate. The 10 to 15 millimeters of movement happens in milliseconds, simultaneously with the foam compression. What changes is the rotational energy your brain absorbs, something you’d only appreciate in the severity (or absence) of a head injury.