The undersuit had armor plates layered with kinetic damping gel, all over an impact dispersion sub-structure and WayneTech biomechanical support technology, protecting against slashing weapons, blunt trauma, and most firearms. The first Batsuit consisted of a heavy amount of kevlar padding centered around the chest area.
He ended up taking pieces of tech either that he invented, fabricated, or things from the Wayne Enterprises facilities, and ended up 'cobbling' all the pieces of tech that he could gather into his first suit. When first preparing for his war against crime, Bruce Wayne realized that he would need a diguise that not only concealed his identity, but could also provide adequate protection from any threats that he might've gone up against and make him look formidable.
Bruce used this suit to inspire fear since he was already much faster, stronger, and more powerful then any ordinary human could ever be- it made him seem otherworldly. They stalk their prey, observe intently, then swoop in to strike. Bats are hunters, mysterious and unpredictable.
