P2453BTA microspheres are solid glass spheres made of barium titanate glass that have been hemispheric ally coated with a thin aluminium shell. The high refractive index of barium titanate glass combined with the aluminium coating on half the glass sphere provides the mechanism for retro reflectivity since light passes through the clear half of the sphere and “bounces” off the aluminium coating. The light reflected from the sphere’s surface returns directly back to the light source or viewer, resulting in greater visibility in dark or night time conditions.