3D printing technology provides an affordable method of prototyping antennas. To design antennas with this technology it is necessary to characterize the materials used for printing precisely in terms of their permittivity and conductivity. Two major groups of materials for antenna design are dielectric and conductive materials. In this paper, we consider measurement of dielectric constants of three types of polylactic acid (PLA) plastic materials that can be used for 3D printing of antennas and other radio frequency (RF) devices.