You only had 3 (if I remember correctly) item categories that gave you resistance - jacket, pants and boots. The rest of the clothing had no effect. Now only the boots are listed as having an effect, but I’m not even really convinced they do anything.
As far as I could tell (this is definitely a subjective observation on my part), the 3 items were cumulative. If you went all bullet resistance (what I ultimately did), you’d be reasonably hardened to bullets. I tried combinations of stealth, explosion and bullet, and that decreased my bullet resistance quite a bit, causing me to go back. Most of the attacks we take are from bullets, so that made most sense to me.
When I really noticed just how much protection clothing offered was after the 1.03 patch that broke the clothing system. At that point, I was getting shredded and killed by groups of runners that I would normally be able to tank and fight off without issue. After that I had to readjust my play style to accommodate for being far more squishy than I was with protection.