The camail, sometimes called an aventail, is a skirt of chain mail hanging down from the cervelliere.
This image from the Manesse manuscript, which is dated around 1330, shows the camails hanging below the cervellieres on these knights.
Chain mail is easy to make, but time consuming. I bought a whole-head chain mail coif on eBay from Sterling Swords and removed the crown. Then, I wove the links into a leather strap with holes to fit over the vervelles. I plan to replace this with riveted mail to match my hauberk.