IN ONLY A FEW YEARS, silky merino wool has gained acceptance as a true performance fabric, standing alongside advanced synthetics in cold-weather mid- and base layers. And now it's challenging cotton for space in your T-shirt drawer. Companies like New Zealand's Icebreaker and Steamboat Springs, Colorado–based Smartwool have spun fabrics that apply wool's natural breathability, wicking characteristics, and odor-fighting properties to featherweight summer styles. It's an old idea that's new again—up until the early eighties, Tour de France jerseys were made of wool. But unlike those scratchy tops of yore, today's high-quality merino fibers, some married to more durable nylon, are one-fourth the width of a human hair—meaning no itchiness and smooth style. If it's good enough for an Italian suit, it's good enough for your undershirt.

Tee Up
SMARTWOOL
Moto Tee (far right), 100 percent wool; $65; www.smartwool.com

IBEX
QuT (far left), 100 percent wool; $79; www.ibexwear.com

OUTDOOR RESEARCH
Sequence T (left), polyester and wool; $35; www.orgear.com

ARC'TERYX
Emissary (right), 100 percent wool; $80; www.arcteryx.com

ICEBREAKER
Superfine Elite T (not pictured), 100 percent wool; $89; www.icebreaker.com

MACPAC
Interwool Mountain Versatile Tee (not pictured), wool-polyester-spandex composite; $55; www.macpac.co.nz