When Americans think of hill climbing prizes, KOM (King of the Mountains) comes to mind. In Italy, the prize is GPM, Gran Premio della Montagna. Castelli's GPM Full Zip Jersey is a fine maglia to wear when scooting up steep hills to steal mountain points from your friends. You love them, but sometimes you have to beat them. It's for their own good.The GPM is probably the least flashy jersey in the Castelli lineup, but it still stands out with the classic close Castelli fit, grey caps on the sleeves and collar, and of course, their scorpion logo.The GPM Jersey is similar to the Prologo jersey in terms of fit and material. The differences are that the GPM uses 100% Stratus fabric with Prosecco treatment. There are no contrasting color panels, the collar and sleeves are topped with seamless micro fiber fabric for comfort and grip, and there's a silicone gripper at the waist hem. Castelli also thought to include a full-length zipper (FZ) with a cam-lock on the pull. Open up the zipper and you can pull open the jersey without tugging on the zipper. Lock down the cam, and the pull will stay in place.Castelli's Stratus fabric with Prosecco treatment looks simple. But the engineering behind it is impressive. Stratus is a dual-layer 100% polyester knit weave. The inner layer is a multifilament web that moves moisture from your skin or base layer to the outside of the fabric. The outer layer is a micro fiber weave that allows sweat to evaporate in the wind. Prosecco is a treatment that helps water disperse and evaporate faster, rather than staying in the jersey. There are three standard rear pockets with the Castelli scorpion on the middle pocket and a fourth, mini-zip pocket built into the right rear. The Castelli logo is also on the shoulder.The Castelli GPM Full Zip Short Sleeve Jersey comes in Black, Cyan, Red, and White. Sizes run from Small to XX-Large.