(Link) All materials reflect and refract light, which is to say all materials alter the angle of light. The higher the refractive index, the higher the light intensity reflected from the surface. Titanium dioxide has a refractive index of 2.7, one of the highest of all materials, and diamonds are about 2.419 – and we know how sparkly they can be! – whereas water is around 1.33. This is super relevant in hair care products. If you want shine to your hair, you’ll want to choose ingredients with higher refractive index levels. Dimethicone has a higher level than cyclomethicone, so adding more dimethicone to an anti-frizz spray will increase the shine on your hair.