King Arthur somewhat over-metaphorically says...
American flour has a type A personality. It’s full of gluten, ready for action, go go GO! Italian 00 flour, on the other hand, mirrors the warm, laid-back climate of its native land. Its protein is not only lower, but much more mellow. Make pizza or flatbread with this flour; you’ve never worked with such friendly dough! It’s incredibly extensible, practically flowing under your hands as you pat it into shape. And the resulting bread or crust? Light as air, tender, snapping crisp or soft as a cloud… this flour is definitely personality type B.