Some polarization properties of reflection-type photopolymer are investigated. The Mylar substrate alters an incoming linearly polarized laser beam to an elliptical polarization. The extinction ration is of the order of 1 to 3.7 for the tested samples. Polarization effects are found to change over different regions of each sample by approximately 10 to 50%. The Mylar substrate alone was found to distort the incoming polarization to a comparable degree. By aligning the position of the photopolymer to have the maximum amount of light passed through the analyzer, it is possible to make stabilized gratings with uniform diffraction efficiencies.