Choosing a lightweight layering system for high-altitude backpacking can be a pain. Weather changes quickly in the mountains, and it's not uncommon, if you're gaining and losing altitude, to encounter sunshine, rain and even snow in the same day. Enter Sierra Designs, with its fully integrated Cloud Layering System. The Windshell (6 oz) serves as a good go-to hiking jacket; add the paper-thin, waterproof, breathable Airshell (4 oz) when the sky opens up; and the DriDown-equipped Puffy (12 oz) keeps you cozy when temps drop and flakes start to fly (it's fairly waterproof in its own right). The whole system packs up very small and weighs in at a diminutive 22 ounces.
$493 complete system ($119 for Windshell; $249 for Puffy; $125 for Airshell); sierra designs.com