Adamantine

A fine example of human ingenuity, it was invented during the later part of The Age of Unity as a material able to withstand rapid arrow strikes from the Orc bowmen hordes. Adamantine was initially an attempt to recreate the legendary Mythril, and instead humans managed to create a metal that is sturdier than its elven cousin but not as heavy as Deep Iron. Adamantine could be described as a general upgrade to steel and exists as an expensive premium material for wealthy adventurers. It's also highly valued for its armor-piercing abilities.

Sancha Gobzales inherited her helmet from Siegfrieds's buckler shield gifted by Flayne la Karrotte, which was made from Adamantine. Of course she isn't aware of this fact, as she would never be able to afford such a prized piece with her squire's salary. This buckler shield was also Jeanne's.