Beskar'kandar

"Although it is nearly impervious to a lightsaber blade, it is extremely heavy and requires the wearer to rely on a Strong style, or djem so, combat stance."

- Darth Bane

Beskar'kandar was a type of Mandalorian armor comprised of plates forged from beskar iron, a near-indestructable ore found only on the planet Mandalore and it's moon, Concordia. The beskar used in the armor's construction made it almost impervious to the blows of a lightsaber. However, the Sith Lord Darth Bane—who wrote a brief passage on beskar'kandar armor in an essay entitled The Rule of Two—found the armor to be extremely heavy, and noted that any Sith who may consider utilizing the Mandalorian armor should adopt a Strong or Djem So stance while in combat.

Behind the scenes
Beskar'kandar was first introduced to Star Wars canon in the 2012 reference book, Book of Sith: Secrets from the Dark Side, by author Daniel Wallace.