The outer shell gets all the glory, but the piece that decides whether your day goes well is the one you pull on first. A base layer is the next-to-skin part of the system, the thing that sits closest to your body, manages sweat before it turns icy, and traps just enough heat to keep you functional instead of furious. Get it right and your back stays warm on the lift, a skintrack sweat never becomes a shiver, and an overnight flight feels marginally less like a hostage situation. Get it wrong, and you spend the day in a damp, clingy, synthetic regret sock.

For most guys, “base layer” now means a whole category, not just long johns from a ski shop. There are close-cut tops that disappear under a shell, hooded layers that double as sun protection and makeshift balaclavas, and bottoms that sit cleanly above your ski boots instead of balling up in your socks. What qualifies them as base layers is simple: they are designed to be worn next to skin, to wick moisture away from it, and to work under at least one more layer without bunching or fighting your jacket.

Fabric is the other big variable. Merino wool handles odor and all-day wear. Synthetics dry fast and take abuse. Blends try to borrow the best traits from both. Most brands list a GSM (grams per square meter) number, which essentially represents the density of the fabric. Lower GSM feels lighter and cooler, while higher GSM feels thicker and warmer. The point of this guide is to cut through the noise and match the right tops, bottoms and hoodies to the way you actually live in winter, then build the rest of your kit around that first layer.

If you only buy one base layer top, make it this one. The Classic All-Season features a light 150 GSM merino-nylon blend that feels soft, breathes well and repels odors in a way........

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