With just a base layer it's a wind-protection jersey for mild conditions. Alternatively, use it like a vest over a jersey with added protection over your shoulders. Lightweight, breathable front wind protection with allover water repellency.
Lightest Castelli short-sleeve wind protection
GORE-TEX INFINIUM™ WINDSTOPPER® 203 Stretch lightweight fabric on front and sleeves
Nano Flex Light Woven on back for breathable stretch with good water protection
YKK® Vislon® zipper for easy ventilation adjustment on the fly
2 rear pockets with pump sleeve
Gabba-style dropped tail with reflective panel