Alpinestars SM3 Radium Helmet

• The SM3 Radium Helmet is designed primarily for MX (motocross), Enduro, and off-road riding. Alpinestars+2Rocky Mountain ATV/MC+2

• It’s built to deliver a blend of lightweight performance, comfort, and impact protection, suitable for aggressive and challenging off-road conditions. Santa Clara Cycle+2Alpinestars SpA+2

🛡️ Construction & Materials

• The outer shell is a thermo-injected polymer blend, with variable thickness designed to balance impact protection and lightweight feel. Alpinestars+2Rocky Mountain ATV/MC+2

• It uses a multi-density EPS inner liner (five EPS liner sizes, with four different densities) to optimize volume, comfort, and impact absorption. RevZilla+2Rocky Mountain ATV/MC+2

• The interior includes removable cheek pads and crown liner. These can be swapped out for different thicknesses, allowing for a more tailored fit to the rider’s head. Rocky Mountain ATV/MC+2RevZilla+2

• The cheek pads even have channels for hydration tubes, which is a convenience feature for long off-road or endurance rides. Rocky Mountain ATV/MC+2Alpinestars+2

🌬️ Ventilation & Comfort Features

• The helmet is configured with 10 air inlets and 7 exhaust ports, giving maximized ventilation and heat exchange — important for strenuous riding or hot conditions. Alpinestars+2Santa Clara Cycle+2

• The liner uses recycled materials, which may matter if you care about environmental impact and sustainability. Alpinestars+1

• Fit customization via replacement liners and pads helps the helmet serve riders with different head shapes or preference for a snug vs. looser fit. RevZilla+1

🔒 Safety & Protection Features

• The helmet includes a patented low-friction coating on the inner part of the main EPS liner. This helps reduce rotational acceleration forces during oblique impacts — an important factor for reducing risk of brain injury. Alpinestars+2RevZilla+2

• A visor release system is built in: the visor is engineered to release under predetermined force to reduce neck strain in a crash. Alpinestars+1

• The helmet’s chin area and shell thickness have been optimized beyond just the standard homologation requirement for better impact performance. Alpinestars+1

• Safety hardware includes a 25 mm soft textile chin strap and stainless steel D-rings for a secure fit. Alpinestars+1

• The helmet is certified to both DOT and ECE 2206 standards, making it compliant for use in many regions worldwide. Alpinestars+1

⚙️ Fit & Sizing Details

• For a medium-sized helmet, the typical weight is about 1430 g (ECE version) and 1460 g (DOT version) — a reasonable weight given the protective features. Alpinestars+1

• Sizing follows standard head circumference: e.g. XS = 53–54 cm, S = 55–56 cm, M = 57–58 cm, L = 59–60 cm, XL = 61–62 cm, 2XL = 63–64 cm. RevZilla+1

🎯 What makes it stand out

• Good balance between lightweight feel and robust protection, which helps reduce fatigue on long rides while maintaining safety.

• High ventilation — beneficial during intense off-road riding or in hot weather.

• Rotational impact protection — a relatively advanced safety feature that many helmets don’t standardly include.

• Customizable fit and comfort — useful if you care about a helmet that feels right on your head and stays stable during rough rides.

• Global certification (DOT + ECE) — makes it versatile if you ride in different regions or plan international use.