It’s important to understand that, as formidable as Darth Vader’s armor may be, its main purpose was to keep Darth Vader alive. That means it was constructed of fairly common substances in the Star Warsi galaxy, with a plastoid girdle and a plasteel helmet - lighter to allow Darth Vader more mobility. The bulk of the armor, though, was composed of durasteel - a metal alloy used for everything from combat armor to construction.

Durasteel is nowhere near as tough as the Mandalorian alloy beskar, but it is still tremendously durable. It’s stronger than standard steel but weaker than titanium, able to absorb kinetic energy with minimal damage, and it’s often used for defensive plating on starships. Darth Vader was able to use the durasteel to his advantage, adopting a more savage lightsaber form that took advantage of his hydraulic limbs. The durasteel absorbed the energy of his blows if they were blocked, meaning he didn’t feel any strong impact.

Darth Vader’s armor also contained obsidian, which perhaps explains the traditional black color. Obsidian is a volcanic mineral-like substance commonly found around active volcanoes, and it was likely in plentiful supply on Mustafar, the planet where Darth Vader was truly born and the world that became his base of operations. Obsidian can be infused with the dark side of the Force, and can even be charged to power lightsabers.

.Darth Vader was phenomenally powerful in his own right, but the obsidian in his armor would effectively supercharge his dark side power. The obsidian would naturally absorb the anger and hatred of the Sith Lord, turning it into a battery he could draw upon. It’s certainly typical of the Sith to turn a life-support unit into a weapon.