A helmet structure including a transparent shell. The transparent shell including a matrix of ventilation apertures coextensive with the shell. The shell further including a visor mounted at a forward end thereof overlying a forward facial opening, including lateral ventilation ports positioned coextensive with the visor laterally displaced side edges. The shell includes a multi-layer construction, including an inner and outer transparent layer sandwiching a central laminate layer of photochromic material to accommodate various environmental lighting conditions. A modification of the invention includes a further inner layer defined by an inflatable transparent polymeric material, including a squeeze bulb to direct air interiorly thereof to accommodate individuals' varying cranial geometric configurations, as well as providing an enhanced safety layer within the helmet structure.