Silkworm cocoon silk and spider major ampullate (drag line) silk exhibit macroscopic tensile properties that, while impressive in the context of polymer fibers, are highly variable. The variability is linked to the cross-sectional geometry being nonuniform : silk fiber cross section changes significantly over distances that are small compared to the scale on which diameters are averaged by typical characterization techniques. This characteristic must be taken into account when evaluating chemical treatments (in the present case infiltrating with crosslinkable epoxide) that are aimed at improving strength or stiffness. The magnitude of any change in mechanical property must be considered in relation to the spread in values recorded prior to treatment. An apparent improvement in the mean value of a tensile property may turn out to be statistically insignificant when compared to the standard deviations associated with those data. Previous authors do not address this simple assessment of significance.