Characterizing PCB materials for Dk and Df of the dielectric materials, as well as the surface roughness can be challenging. A typical build will often have core and pre-preg materials with Dks that can vary by 10-15%. For low loss materials with Dfs less than 0.005, extraction of Df can be difficult. Further, separating the dielectric loss from the surface roughness loss adds to the complexity of characterizing the losses. This presentation will give examples of different behaviors in the S-parameters and single-bit response of materials for loss, and multiple Dks. Then an approach for characterizing the materials will be presented.