It claims this is 4" ducting... which is the same size as "normal". but with the coating, it's not as flexible or easy to get on to the dryer or the exhaust vent or the 4" air box we have in-line to help prevent back-draft from the outside vent. I was able to get it on, but it was MUCH more difficult than I anticipated.
Given that, once it was in place, it stayed there. The clamps were easy to get on. I don't feel anything escaping from the ducting and it was more than long enough to reach from my dryer to the air box. I think that, despite the difficulties in getting the ducting on the dryer and outside vent, it is definitely worth it. Great price, long enough to work in my basement laundry room and looks/feels sturdy enough to last for years.