I'm not sure, I'd say the leather? When it's empty it's not heavy but when I start putting my stuff in it, I don't overfill, my shoulder is crying "uncle" after a trip to the mall. Ugh. I switch Gigi to my other shoulder so frequently that I can't concentrate on anything else but the dull, nagging pain.Oh that's not very sexy thenSo what makes them heavy? The leather or hardware?