The quasi-optics of mm waves have been investigated in the context of reflection by typical wall materials. The Brewster angle phenomenon is prominently manifest when the magnetic vector is parallel to the surface. Even the complex structure of materials such as brick or plywood display such effects thus showing that the idealised theories of classical optics provide valuable guidance for the mm wave wireless LAN designer. The Brewster angle has also been used to determine the effective dielectric constant of both pure and composite materials