Mandalorian beskar armor is the only material in Star Wars that can stop a lightsaber.
There is not much stronger than Mandalorian armor. Blaster shots bounce right off of it, and it can even withstand a strike from a lightsaber. Mandalorian armor is so strong because it is made from beskar, a rare and immensely strong metal in the Star Wars universe. But how strong is it?
To answer that, it is best first to understand its place in the galaxy.
Also known as Mandalorian Iron, beskar is a rare metal ore that can only be found naturally in the Mandalore system. The Mandalorian culture is one of warriors, and over time, they perfected a method of forging beskar that allowed them to increase the strength of the rare metal and shape it into various items.
In the Mandalorian culture, it is inappropriate to craft weapons from beskar; instead, the metal is used primarily to forge nearly indestructible armor for its warriors. Mandalorians consider beskar to belong to them, so when it falls into the hands of outsiders, they do not react kindly.
That is for a good reason. The only thing that can pierce Mandalorian armor is a weapon also made from beskar, which is why they do not practice making weapons from the precious metal.
Mandalorian beskar is one of the few things in the galaxy that can hold up against a lightsaber. In Season 2 of The Mandalorian, Din Djarin deflects several lightsaber strikes from Ahsoka Tano using the beskar armor plating his forearm.
To let that sink in, consider all the things that lightsabers have cut through over the course of Star Wars canon. Blast doors, Kylo Ren’s ship, tauntaun bellies, Skywalker limbs…
Okay, not all of those are especially tough, but some of them are designed to be tough, and lightsabers slice them all. A thin plate of Mandalorian armor can bring a lightsaber strike to a dead stop, but beskar does have its limits.
When heated to the right temperature, beskar can be liquified and reformed. A lightsaber could heat beskar enough to cut through, given enough contact. Repeated contact with lightsaber strikes can also cause beskar armor to break, but it can buy you more time against a lightsaber than almost anything else in the galaxy.
Another way to beat beskar is a weapon called the Arc Pulse Generator. The weapon does not really even beat the beskar; it just targets it and vaporizes whoever is wearing it. Developed by the Empire, the grisly weapon killed many a Mandalorian by turning the strength of wearing beskar against them.
Even with technology like the Arc Pulse Generator out there, beskar is still able to withstand anything else within reason. So, if beskar is so strong, why not make everything out of it?
As mentioned earlier, the Mandalorian people are possessive when it comes to beskar. The metal belongs to them, and they do not like to share.
Beyond that, beskar is extremely rare. In a very large galaxy, beskar only originates in one place. Because of its rarity and unparalleled functionality, it is a high-value item on the black market.
During the reign of the Empire, smuggling beskar was a particularly profitable endeavor. Stolen and traded beskar, raw or forged, has spread through the galaxy. But where beskar goes, trouble usually follows.
Many have tried to replicate the forging techniques of the Mandalorian people, and just as many have failed to use beskar to the same effect. The ancient warrior culture alone carries the secrets of smithing beskar to its full potential and thus holds the key to harnessing one of the strongest materials in the galaxy.