Bontrager Sport Wind Vest
Pack along Bontrager's Sport Wind Vest on every ride and you won't be sorry. Made from ultralight microfiber that's both wind and water resistant, it packs down super small to easily fit in your jersey pocket, not bothering you until you need it. And, it's made specifically for cycling with an on-bike cut and reflective accents throughout.
This manufacturer's chart helps you evaluate the fit (may show unavailable, and/or not all sizes).