Outdoor shell helmet

 The shell helmet is a durable, traditional helmet, offering a solid exterior supported by an interior that features a strap system of cross-tensioned straps. The ventilation of shell helmets is generally good because there is air between the shell and the head. Impact energy is primarily absorbed by elastic deformation, ie the exterior deforms on impact and then, in most cases, returns to its original shape. This absorbs the energy of a vertical impact, such as a falling rock. Scale models are particularly durable, but relatively heavy.