.When unpolarized light hits a reflective surface, the vertically polarized aspects are refracted into the surface. The horizontally polarized aspects are reflected off the surface and the light is now perceived as partially polarized.
Source: Boundless. “Polarization By Scattering and Reflecting.” Boundless Physics. Boundless, 26 May. 2016. Retrieved 11 Sep. 2016 from https://www.boundless.com/physics/textbooks/boundless-physics-textbook/wave-optics-26/further-topics-176/polarization-by-scattering-and-reflecting-643-6054/