Best overall
The shirt you wear for eight days without anyone minding
Icebreaker Merino 200 Oasis Long Sleeve Crew
200 g/m² merino, mid-weight
Merino at 200-weight is the one true trekking base layer — warm damp, warm dry, and it does not smell; it is also three times the price of synthetic and it will eventually hole at the shoulder where the pack rubs.
No smell after a week, which is the whole argument
Still warm when damp with sweat
Comfortable next to skin with no itch at this weight
Expensive
Wears through at pack-strap contact points
Slow to dry compared with synthetic
Not for you if: A four-day trek where you can wash and change. Synthetic is cheaper, tougher and dries faster; merino earns its price on long trips without laundry.
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