When it comes to travel apparel, you're best off relying on clothes that heartily mix form and function. And while some of the pieces below may run against standard outdoor-oriented conventions (aka: cotton kills), each hand-selected item will keep you in pace with the world's fashionistas without sacrificing a stitch of travel-essential asset: reliable performance and undeniable comfort.

Tops
Smartwool has been keeping your feet warm while hiking, skiing, and lazing around hotel room, but now they've their expertise in merino wool has branched out into lifestyle apparel, and the results couldn't be better. Take the Chutes Crew, a buttery-soft heather-colored crew-neck sweater with contrast piping on the shoulder seams, or the women's Basho Celedon, a form-fitting aqua v-neck sweater with striping on the sleeves. Like all Smartwool products, both benefit from merino wool's wicking, odor-free attributes, making ‘em equally at home on the slopes or the tarmac. ($80 each; www.smartwool.com)

For mid-layer versatility, vests really are a go-anywhere, do-anything item, especially when they're two-faced. No, not two-faced like the friend you caught smooching your crush behind the bleachers in tenth grade. Two-faced like reversible. Wear Prana's Reversible Quilted Vest with the plaid, wool face showing to evoke a casual, playful look. Heading to dinner and no time to go back to the hotel? Turn the vest inside out to reveal a more sophisticated, slick nylon face. The vest hits just below the natural waist and has functional pockets no matter how you're sporting it. Whether you wear the vest alone during transitional seasons or as an extra layer under a jacket in winter, you'll get the right amount of warmth at your core without the typical bulk. ($85; www.prana.com)

Base layers (a.k.a. T-shirts), meanwhile, offer an opportunity to reveal your good humor and suave fashion sense. Take Topo Ranch . The California-based apparel company's name evokes the American West, while its graphics lend themselves to both the days of old and the intellectual invention of 1920s surrealist art, such as Max Ernst's woodcut collages—if he happened to raid your kitchen cabinet. All-cotton whimsical creations such as the Can You Ear This men's T-shirt and Butter Heart Tree woman's tee evoke the perfect degree of eco-friendliness without resorting to wearing socks with your sandals. Its signature hoodies, shirts, and jackets are soft enough to make all other clothes feel like burlap, and the high-quality craftsmanship also cuts down on the sloppiness that can otherwise curse the layered approach. (Starting at $36; www.toporanch.com)

Bottoms
The environment-friendly company Nau continues to strive toward apparel perfection—sans the sweatshops—and its Twill Cargo Pants make for a svelte, modernist version of traditionally baggy cargo pants. Twin zipped pockets cut across each thigh to offer storage for passports, plane tickets, and various electronic accessories without making it look like you're smuggling a 400-page guidebook. And a small amount of spandex woven in with the organic cotton gives you just the right degree of stretch and flex. (Available for both men and women for $95; www.nau.com)

Feet and Head
Athletes quickly realize that specialty footwear can swallow the lion's share of a suitcase—typically pushing you from carry-on to rolling duffel. Bless the gods of simplicity (or perhaps just Salomon), then, for the SpeedCross 2. This Outside Gear of the Year winner is one of the lightest, most durable trail runners on the market. The shoe's a glorious mix of paradoxes: nearly weightless yet tough as a tank, shock-absorbing yet still firm, waterproof yet thoroughly breathable, and—perhaps most important to travelers interested in multi-tasking apparel—fashionably sleek and completely functional. ($110; www.salomonsports.com)

For trickier climes, boots become an integral part of most women's winter wardrobe. They look great with skirts and pants, and they add extra warmth on the chilliest of days. But when you're trying to pack everything you'll need for a trip in a 22-inch rolling suitcase, your boots don't always make the cut. Enter Simple's Toetally Boots. Made of organic cotton and linen, bamboo, and molded latex, these boots are not only lightweight and flexible, they're very eco-chic. The natural crepe rubber midsole and the gentle massaging beads in the foot-bed make the Toetally a good candidate for a day of museum hopping. Be aware, however, that the boot doesn't offer much arch support—an after-market insole could likely solve this problem for most people. The Toetally boots are part of Simple's Green Toe line, a company initiative to make fashionable, sustainably-produced shoes for men and women. So you can feel as good about wearing them as you look in them. Buying tip: If you plan to wear these with thick socks, order a half size up. ($120; www.simpleshoes.com)

One essential gear item that won't swallow space in your luggage, however, is a pair of sunglasses—but that may not stop you from packing a few pairs. To resist, go for the Oakley Hijinx. The slightly oversized frames provide a sleek, wrap-around style that'll fully shield you from the sun (and hide bloodshot eyes as you rush from the club to catch the a.m. train). The polarized lens protect your peepers and deliver diamond-sharp vision with the incomparably successful optical technology for which Oakley is now (justifiably) famous.($145; www.oakley.com)