Examples from the Web for underfur
The width of a hair in the underfur is of no taxonomic significance, in that individual variation exceeds that between species.
In mice in the earlier stages of adulthood, underfur of the dorsum is buffy at the tips and gray basally.Speciation and Evolution of the Pygmy Mice, Genus Baiomys|Robert L. Packard
More than 200 impression slides and whole mounts of guard hair and underfur were prepared.
The guard hairs and underfur differ in different species (see figs. 35-37).