The most widely accepted answer is: not much. Daredevil's uniform is more or less a spandex bodysuit with kevlar patches imbedded between layers of spandex over strategic areas for a little added protection without impeding freedom of movement. In other words, it's reinforced clothing, adding about as much protection as the kinds of clothing that bikers wear (maybe less). Good for blunting a punch or the edge of a knife, maybe, but unable to stop any kind of bullet. Now, some sources say that Daredevil, later in his career, acquired a uniform made of unstable molecules. He probably would have had to buy such a uniform from Reed Richards, Mr. Fantastic, since the substance is one of his inventions, and he seems to be the usual source for it. Costumes made from unstable molecules adapt to the superpowers of their wearers; UM costumes are the reason Richards doesn't stretch right out of his costume, and the reason the Human Torch doesn't burn his costume and show up naked every time he turns the flames off. UM costumes also provide considerable protection for their wearer, roughly equivalent to a kevlar vest, with no restriction of movement. Unstable Molecule costumes are the best a superhero can get without upgrading to powered armor. When would Daredevil have acquired such a special suit? Probably during one of those big summer crossovers where all the heroes work together to solve a huge crisis. That's pretty much the only time Daredevil would be likely to hang out with Mr. Fantastic. There is one other special thing about Daredevil's costume: the little horns on his head. This fact has mostly been ignored, but originally, those little horns were actually miniature metal antenna that allowed Daredevil to use his radar-sense to pick up and listen to radio waves. Honest. Superhuman hearing plus little horns on your mask equals a built-in police scanner! I think it's a neat idea, anyway. Oh, one more thing: remember Dardevil's original red and yellow costume? In Jeph Loeb's "Yellow" series, it was revealed that that first costume was made from the boxing robes of Matt Murdock's murdered father, the same robes he wore into the ring for his last fight. Which adds all sorts of symbolic significance to that costume.

It's super-tight.