Midweight base layers (180–260 g/m²) are the most popular pick for dedicated skiers because they hit the sweet spot between warmth and wearability. They provide enough insulation to keep you comfortable during cold lift rides without feeling bulky under your mid-layer and jacket.
This weight class really shines on cold resort days between 0–20°F, especially if you tend to run cold or spend more time sitting on lifts than charging hard down the mountain. The extra fabric thickness traps more body heat than lightweight options, making those long, windy chairlift rides much more bearable.
The trade-off is that midweight can overheat you during aggressive, non-stop skiing or high-output touring. If you ski hard and generate a lot of body heat, you might find yourself unzipping vents constantly. In that case, a lightweight base layer is usually the better call. But for most resort skiers who take breaks and ride lifts regularly, midweight is the reliable go-to.