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Damping loss factors are evaluated for honeycomb composite beams with differ ent configurations of particle damping . Damping effectiveness is evaluated in two ways. First, measured frequency response functions are used in a conventional, polynomial curve -fitting modal method to evaluate damping loss factors at several natural res onanc es in the low frequency range. Secondly, the power input method is applied to evaluate damping loss factors over a broad frequency range. Both damping estimation methods (modal method and power input method) yield consistent loss factor estimations. The effect of different damping configurations has been studied, showing substantial differences in loss factor. Most interestingly, loss factors as high as 0.1 9 have been measured, corroborating reports by others. Further, a simplified fluid model of t he partially -filled honeycomb cell has been found to predict the frequency band of peak damping . This technology then, shows the potential for designing high levels of damping in distinct frequency bands, which is of interest for aircraft interior noise su ppression.