In general, the majority of our phantoms are made of Lucite  (Polymethyl Methacrylate). This material is also known as Perspex  and Plexiglass. Information concerning the atomic number, density and composition of Lucite  can be found here on the web site of the National Institute of Standards and Technology (NIST).MMA has a density of 0.94 g/cm3. The systematic name is methyl 2-methyl-2-propenoate. Its molecular formula is H2C=C(CH3)COOCH3.Information about polycarbonate can be found here, which is also a URL at NIST.