The Castelli Men’s Fly Jack-sey is for those days when you aren’t sure if you need a jacket or just a jersey with warmers. The Fly Jack-sey hits that sweet spot when it’s in between temperatures while offering protection just in case. It features brand-new lightweight construction with Castelli FLY Fabric Technologies FFT and treated with a water-repellent finish to help keep you dry. All this in a super-lightweight piece.