What you should know: When it's warm or you're working hard on a hike, much of the time all you need is this insulating layer over your base. It needs to be lightweight and able to move with you.

Our pick: The Patagonia Capilene 3 Midweight Zip-Neck. The recycled polyester layer is warm and quick drying yet stretchy enough for easy movement. [$41; patagonia.com]