1 crochet hook, 2.75 mm
at least 375 yards of 5mm medium weight acrylic yarn in colors approximating hair, preferably in multiple similar colors
1 sheet of plastic canvas, at least 10.5"x 13.5", grade 7 mesh
~18 inches of slender elastic (a cut-open elastic hair wrap works great)
Time: 3-4 hours
Step 1: Yarn and Plastic Canvas
I used acrylic because wool is too itchy. You want to have at least 375 yards in total but I'd recommend buying a couple smaller rolls, and mixing 2 or more similar colors, even different dye batches of the same color. Beards have varying colors so it adds texture and depth to use a variety of similar shades.
Underneath the label is a leftover strip of the plastic canvas the beard substrate is made of.
I picked brown so it wouldn't stand out much from under the yarn but it comes in other colors too. It cost about $.50 for a sheet and you only need one per beard. Using this stuff saves you the trouble of needing to learn to knit.
It's also sturdy enough to be a solid base, but still easy to cut with scissors.