Can I wear a lightweight base layer for backcountry touring?

Lightweight base layers are actually the preferred choice for backcountry touring because the high-output skin track generates significant body heat and sweat. The superior breathability and fast drying of lightweight options prevent the moisture accumulation that heavier base layers cause during climbing. Many tourers use a lightweight base layer on the ascent and add a mid-layer for the descent. A half-zip top is especially useful for touring because you can open it on the climb and close it for the descent.