Chainmail was made by linking together thousands of small metal ringlets. These ringlets were forged from tiny strips of iron and later steel, with the rings joined in a specific pattern and then closed by pressing, welding or riveting.
The pattern the ringlets were linked in determined the type of mail that was produced. The popular four-in-one design (ie each non-edge ring connecting to four other rings) typified European mail, while six-in-one patterns were more common in Asian mail.
The size of the rings – both in diameter and width – was also important, with larger rings covering a bigger area with less material (and therefore being lighter), yet having a coarse finish. Smaller diameter rings, on the other hand, granted a finer finish and a stronger mesh, but would weigh in considerably more.
The major benefits of chainmail over the solid cuirasses which had been worn in battle prior to its invention were a greater degree of movement for its wearer as well as more extensive coverage (ie arms were protected too). However, chainmail also suffered from a notable weakness in that sword and spear tips, or arrow heads, could penetrate individual ringlets at a direct-on angle. As such, knights would commonly wear a cuirass over the chainmail shirt for extra protection.