Absolutely amazingly cool - you don't know you are wearing it. The material lets air pass through it (aertex/mesh type) and with the loose sides it is a pleasure. It can come with a waterproof and secure pouch so you can take your phone/car keys, wear a tshirt and your lightest breeches - or even shorts! And you will be seen.
Trademark PASS SLOWLY and the speed camera logo as normal.