What you should know: Your last line of defense against the elements. Wear it over the base layer during high-aerobic wet-weather activities or atop the entire system when cold. Must be light, easy to pack, and, most important, breathable.

Our pick: The 17-ounce Westcomb Apoc. Rain easily beads off this shell, which is one of the most breathable we've ever worn, thanks to Polartec's NeoShell fabric. [$480; westcomb.com]