Technical Abstract: Beard method is used for sampling cotton fibers to generate fibrograms from which length parameters can be obtained. It is the sampling method used by HVI. HVI uses a fiber comb to sample cotton fibers and form a fiber beard for measuring fiber length parameters. A fundamental issue about this sampling method is its bias. There have been different assumptions regarding the bias of the beard sampling method. The original fibrogram theory for the beard method adopted an assumption that this procedure is length-biased, while other researchers later revised this assumption to that each fiber has equal probability of being sampled regardless its length (unbiased assumption). In our experiments, we have seen discrepancies in measurements that cannot be explained by using length-biased or unbiased assumptions, especially in the short fiber region. Therefore, it is important to investigate the bias of the beard method. We report a fundamental research, including experimental and theoretical analysis, and computer modeling, that reveals the bias due to this sampling method. We found that the beard sampling method as used in HVI is not completely length-biased; it is very similar to the original sample except in the short fiber region. Short fiber content by number of the sampled fiber is lower than that of the original fiber, and this difference is inherently introduced by the sampling method.