Dual-density foam helmets use two layers of EPS foam with different densities instead of one. The softer layer handles low-energy impacts better, while the firmer layer manages high-energy crashes. This means the helmet protects you more effectively across a wider range of real-world crash scenarios.
Many dual-density designs also include a sliding interface between the two foam layers, providing built-in rotational protection similar to MIPS—but integrated directly into the helmet's structure rather than added as a separate liner. You'll see this in premium systems like MIPS Spherical.
You'll typically find dual-density foam in higher-end road and mountain bike helmets, and it does come at a premium price. For serious riders or anyone wanting top-tier impact protection, it's a worthwhile upgrade. For casual riding, a well-fitting in-mold helmet with standard MIPS will still serve you well at a lower price point.