They are metal clamps but they are also coated in rubber so don't damage the car. I've used various roof racks on previous cars and am also interested in roof carrying options as there is nothing official. I like to keep my muddy/greasy MTB on the outside of the car but don't like boot carriers as they aren't paintwork friendly. There is a couple of forum posters who use boot carriers but I wouldn't recommend. Thule are expensive but it's nice kit and what I've always gone for. I'm trying to find max load figures for the LEAF before taking the plunge this time.