The powder blending process is often identified as a challenging operation in solid dosage form manufacturing. On one hand, inadequate blending leads to poor active ingredient/excipient mixing. On the other hand, excessive blending could potentially deleteriously affect the drug content uniformity the final product. Mixing behavior is complex and can be affected by various chemical and physical properties of the solid materials like density, particle size, particle shape, and surface energy. When large difference in these material properties exists between the active components and excipients, poor mixing effects can occur. In this study, the surface energy values of a model active pharmaceutical ingredient (API), excipient, various physical mixtures of the two, and final capsule blend have been measured and their effects on blend uniformity investigated.