A head-mountable device can provide passive cooling that utilizes surfaces of an optical assembly to allow heat to be managed in a manner that does not detrimentally impact the visual information displayed to the user. Lenses can be coated with a transparent and thermally conductive material, such as silver nanowire. Such a thermal layer can provide superior thermal conductivity, transmittance, flexibility, flat transmission, low cost, and angular color stability. The thermal layer can passively manage heat by increasing the surface area across which heat can be efficiently dissipated.