The Mandalorian's armor may primarily be made from beskar - but it also incorporates elements from elite Stormtrooper armor. Mandalorian warriors are famous across the galaxy, and their armor is highly prized. Even an ordinary human in Mandalorian armor is a force to be reckoned with, as Cobb Vanth demonstrated when he donned Boba Fett's old armor and drove the Mining Guild off Tatooine.
Like all Mandalorian armor, Din Djarin's is primarily composed of a beskar alloy. This is incredibly durable, and Mando has been seen taking direct hits from blaster bolts. In fact, beskar is even able to resist lightsabers, for in The Mandalorian season 2, episode 5, "Chapter 13: The Jedi," both Din's armor and a beskar spear were able to parry Ahsoka Tano's blades. Now that he possesses the beskar spear himself, he's well equipped for if he ever winds up going toe-to-toe with Moff Gideon and the Darksaber.
It seems Din Djarin's armor isn't made entirely of beskar, though. Screen Rant has a copy of Lucasfilm's The Art of The Mandalorian, and in it concept artist Brian Matyas reveals Mando's armor incorporates elements from trophy kills. "I started pilfering from some pieces of designs that I really liked, like the shoretroopers and death troopers," he explains. "Essentially, we've only seen them in Rogue One. I would think they're rare. So, if he has a bounty where he kills one, it's like a trophy." Interestingly enough, though, it seems these trophies have gradually been replaced over the course of the series. Din Djarin obtained a large quantity of beskar for turning in Baby Yoda in The Mandalorian season 1, and this was forged into replacement parts for his armor. She specifically replaces a shoulder pad, which had originally been taken from a Shoretrooper.
This helps explain the lack of symmetry in Din Djarin's armor, because he's continually been improving and upgrading it. It also offers an interesting window into his personality, indicating the strength of his professional pride. Stormtrooper armor may be better than nothing, but it's not exactly strong, as the Armorer proved in The Mandalorian season 1 when she single-handedly took down an entire squad of Stormtroopers.
Din Djarin has acquired a substantial stock of beskar over the course of The Mandalorian season 2, including Boba Fett's old armor and the beskar spear. It's entirely possible he will have an Armorer melt the beskar and add it to his own armor, further improving the suit he now wears. Meanwhile, it's also plausible Mando's continuing feud with the Empire will lead to his adding more trophies to his suit. Whatever the case may be, Din Djarin may well become even more formidable in The Mandalorian seasons 2 and 3, as his armor continues to improve.