Are pull ups an effective way to build muscle mass in the arms?

im 5'6 140lbs. with 16% body fat (is that good?) and i want to build my arm muscles. what type of pull ups should i do? i can already do 10+ pull ups in a row easily. should i put on a backpack with like 20+ pounds in it on my back or what sholud i do cuz i want to build visible muscle in my arms?