Beard hairs are usually thicker than hairs on the head: while the diameters of head hair range from 0.04 to 0.12 mm, the diameters of beard hair are on average twice as big: 0.09-0.23 mm.
However, the structure of beard hair is more similar to the structure of pubic hair: Beard hairs have a thicker shaft, are more rigid, and usually do not grow as long as head hairs. Their hair follicles produce more sebum (skin fat), so that they are good scent carriers for pheromones – e.g. sex attractants.

The image shows a colored beard hair taken in a scanning electron microscope (SEM).
The magnification is 800fold.