The entire sixteen-element light scattering matrix is experimentally determined for a circular cross-sectioned conducting fiber illuminated with lambda = 632.8-nm radiation at normal incidence. The radius (1.552 +/- 0.007) microm, determined by comparison to Mie theory modified for cylinders, indicates that micron-sized fiber radii can be determined within a few nanometers by polarized light scattering techniques. We discuss changes that occur in matrix elements as a quartz fiber is coated with aluminum to form a conducting fiber. Mueller matrices can be used to study time-varying processes, such as water vapor buildup on small particles and surfaces.