Castelli Pro Light Wind Vest was made for Team Sky, for those rides when you need a bit of extra warmth when you head out in the morning or when you go down that long descent to do another interval.
But knowing it'll spend a lot of time in a jersey pocket, Castelli made it as light and small as possible. It weighs just 81g (in size Large), about the weight of two gels, and takes up little more space than those two gels. The back is mesh while the front is a low-permeability woven poly fabric that keeps the wind off without letting moisture build up. No need to underdress ever again.
Impossibly lightweight and compact wind vest
Printed woven front and shoulders with low air permeability to block wind while remaining breathable