Feathers are crucial to survival and reproduction in birds, functioning in insulation, flight, camouflage, and communication. As with most biological structures, form affects function, and the structural properties of feathers affects their performance. One oft-used measure of feather structure is barb density (Bachmann et al. 2007), the number of barbs per unit measure, typically measured at the midpoint of the feather along the rachis. This measure has been used by multiple researchers to characterize structure of the feather and as a means of comparison between species. We will show how the traditional methodology is misleading because it compounds barb density with barb angle, two independent features of feather morphology. Conclusions inferred from the traditional measure are, at best, imprecise, and at worst, wrong. We suggest that both barb angle and barb density measured perpendicular to the barbs be reported and propose an alternative approach in which barb angle is used to compute barb density.