I give it 5-Stars for the Function and Purpose of wind-proof and easy of packability; however, I give it 1-Star for aerodynamics. I could hardly feel it when I was wearing it as it is extremely light weight and virtually wind-proof. The biggest downfall it has it the excess flapping garbage bag sound coming from the material behind your head. The vest creeps up and the loose material flaps in the wind that eventually wore down my tolerance that I determined it was a very expensive Hefty bag. I ended up having to tuck the bottom of the vest under my jersey to minimize the sound which I had to redo periodically.
I purchased the Large, which is the smallest I could get, as the Medium, I could not zip up. Please think seriously before buying this product. I didn't give it a 1-Star because it does work as which it was designed so it doesn't out right suck. I just would like not to recommend it due to the excess noise it creates.