Best Base Layer (2025): Ibex, Smartwool, and More

These soft, stretchy underwear are made from capilene, an insulating fabric spun from 100% recycled polyester. Synthetic yarns have performance comparable to wool. Capilene is also just as comfortable, while being lightweight and quick-drying. Patagonia sells base layers in two weights: a midweight and a heavier thermal weight. They come in men’s and women’s sizes, and the tops are available with a crew neck or a zip neck. I tested them in the fall in Minnesota and San Francisco, so I wore the mid-weight version with a crew-neck top.

Taking advantage of the precision offered by working with synthetic fabric, Patagonia has made interesting design choices. The garments are smooth on the outside and feature a subtly embossed diamond grid pattern on the inside. The company says this diamond pattern creates small pockets that trap heat and help wick away moisture. This claim is almost impossible to verify, other than to say: the fabric kept me about as warm as merino wool.

Like most Patagonia clothing, these are a little looser than other brands of the same size. Although I tend to like my base layers to sit snug against my skin for maximum warmth, I appreciated the extra room here at the shoulders, groin, and under my arms. I wore them for two days straight on a canoe-camping trip – even sleeping in them – and after a wash a week later, two more days commuting to and from my office. They didn’t chafe or bunch, and the elastic points never got pinched. After each multi-day wear, they stank a little – more than wool would in the same scenario, but much better than other synthetics I’ve tried. If you avoid wool due to allergies or because you avoid animal by-products, this fair trade certified two-piece is a solid alternative. —Michael Calore