This work presents the characterization of the effective conductivity of additive manufacturing materials used for the fabrication of high-frequency communication devices. Factors such as material type, porosity, roughness, and oxidation reduce this conductivity, leading to increased insertion loss in the manufactured devices. For characterization, an X-band cavity resonator on a rectangular waveguide was designed, and the quality factor was measured for different implementations using various techniques and materials. Conductivity values of up to 17.70 MS/m were obtained for metallized polymeric materials and up to 6.44 MS/m for metallic alloys.