T-shirt Mérinos Femme 180 Noir Uni | Col Ras du Cou

Warm & hot weather · 60°F+ / 15°C+ — and high effort in any season

Best for: summer hiking, running, cycling, hot-climate travel, everyday tees and office wear; the next-to-skin layer under a 250 when you work hard in winter

Pick this if: you want a shirt that stays fresh for days, dries in an hour and keeps you cooler than cotton in the heat — or you simply run hot

Think twice if: you will mostly be standing still in the cold; on its own a lightweight layer has little insulation to offer

Cool to mild · 40–65°F / 5–18°C

Best for: spring and fall as a standalone top, summer evenings, cool-morning hikes and commutes; winter as a base under a mid-layer

Pick this if: you want one merino layer that covers most of the year, or you are unsure between light and mid — this is where most people should start

Think twice if: you run cold and your winter is genuinely cold: go straight to 250

Cold · 20–45°F / −7–7°C — the classic winter base layer

Best for: skiing and snowboarding, winter hiking, cold-weather work, frosty fall mornings; top-and-bottom sets so your legs are not the weak link

Pick this if: you run cold in fall, want the classic winter base layer, or spend active days below freezing under a shell

Think twice if: you overheat easily on hard uphill efforts — a 165 or 190 underneath, 250 over it, is the better system

Deep cold · below 25°F / −4°C — especially when you stop moving

Best for: ice fishing, hunting stands, camp at altitude, winter mornings spent waiting rather than walking, a house that never quite gets warm

Pick this if: warmth matters more than breathability, you are chronically cold, or your winter involves long spells standing still outdoors

Think twice if: you will be working hard — it is too warm for a sweaty climb, which is exactly the point