Biggins were a type of undercap worn by all classes, ages, and sexes during the sixteenth century. They kept hair in place and sweat from staining hats.

“Peasants and children almost always wore the biggins alone, as they had no other cap. Working classes would frequently wear the biggins alone, but perhaps made from nicer fabric or they might add a touch of embroidery to show a higher standing.”

A padded version of the biggins, the arming cap, was worn beneath the a coif or helmet. It served much the same purpose, but with the added benefit of reducing shock to the head and keeping one’s hair from being caught in mail.

When making my own, I used a pair of old pants which did not fit me for the fabric. I drew out the pattern on newspaper and taped the pieces together to ensure a good fit. After that, I cut out my pieces and sewed everything together on the sewing machine.

If you want to make one, this is the design which I followed when making this piece: https://youtu.be/MimPxme2KAQ

Source: http://www.mistythicket.com/accessories/caps/biggins.html