Fibrograms were obtained for cotton beards used in HVI testing after conditioning the beards in two different relative humidity environments. The differences in optical mass measurements for the fibrograms were negligibly small and close to the resolution of the optical system of the instrument. HVI test specimens from several cottons were tested at three different rates of loading in two different relative humidity environments where the temperature was held to a nominal 70 degrees F. It might be possible to select a rate of loading for HVI systems that would reduce the variations in HVI strength measurements due to moisture content variations. Using a cut-and-weigh procedure, it was shown that fiber surface characteristics have a significant effect on optical mass determinations in HVI strength tests. The optical mass determinations was also shown to be sensitive to the distributions of the micronaire/fineness of the fibers in the test specimens. Scouring to remove or reduce surface constituents was used to demonstrate that natural waxes can cause errors in mass determination made by optical methods. Swelling of the fibers causes significant changes in optical mass measurements, indicating that fiber surface smoothness affects the reflectance properties. International interlaboratory test results show significant fiber color effects on differences in strength measurements using Stelomer and HVI. Dyed fibers were used to evaluate the effect of fiber color on the optical mass measurements made by HVI systems. Significant correlations were found between color parameters and weight estimations based on optical readings. Corrections are possible to minimize the effect of color on optical mass measurements.