Abstract: Hydrophilic copolymers which consist of a combination of hydrophobic monomers (methyl methacrylate, MMA) and hydrophilic monomers (vinyl pyrolidone, VP) have all the required major elements such as hydrogen, carbon, nitrogen and oxygen, found in tissues. They have the potential to be used as breast phantom materials since they can be made to have similar elemental composition as that of body soft tissues. Photon attenuation measurements were performed on dry and hydrated hydrophilic copolymers using X-ray fluorescent (XRF) photons. They were obtained by bombarding copper, molybdenum, silver and tin targets to X-rays from an industrial X-ray tube; effectively producing 8.02, 8.89, 17.41, 19.55, 22.08, 24.87, 25.16 and 28.43 keV photons. The measured mass attenuation coefficients of the samples were compared with the calculated breast mass attenuation coefficients...