Photopolymers have been analyzed as holographic recording materials by measuring their diffraction efficiency in relation to the index modulation that is obtained with these materials, their spatial response and their energetic and spectral sensitivities. However, even though they are considered good recording materials for the storage of information and for the production of holographic optical elements, little information has been offered on the image quality that these recording materials produce. Among the different sources of noise in holography, noise gratings have been analyzed extensively in photographic emulsion due to the granular nature of these recording materials. However, information about photopolymers is quite scare. For material that work in real time, it is the transmittance function which measures the appearance of noise gratings given that the presence of this noise source manifests itself when transmitted light decreases due to diffraction. We present a theoretical model that relates the photopolymer transmittance function response with the noise grating structure. In keeping with the experiments we can say that noise gratings also appear in photopolymers which proves the presence of a certain granular structure in these materials. Their appearance and storage in these materials can be used as a methodology for the optimization of these recording materials. ; This work was partially supported by the CICYT, Spain, under projects MAT93-0369 and MAT96-1767-E.