Best Base Layer?

Hands down Merino Wool. No synthetic has the same thermal range properties as Merino. I like Ice Breaker clothing as well as Smart Wool. Ive worked (and played) in the outdoor industry for nearly 20 yrs and have never found a synthetic piece that could be worn for more than a day without smelling. While trekking in Nepal a few yrs back, I wore the same Merino piece for 3 week and I kid you not, it did not smell. You can even wear your merino to a smokey bar. It will smell when you get home but give it a few hours and the smell will go away. Try doing that with petrol based synthetics! Youll pay more but in theory youll need 75% less garments for the same trip. The Merino also keeps you cooler in warm weather and warmer in cold weather. Its like the thermos of textiles!

I think the best base layer is silk, especially for it's heat holding to weight ratio. I have silk longjohn shirts and pants that I use when backpacking in the Sierra's and they feel great against your skin, provide a nice heat layer, aren't bulky under pants or jeans, and weight almost nothing.

silk weight Merino wool or silk weight advanced wicking clothing. Always silk weight. If doing backcountry style xc skiing, it is always best to be able to wear all your clothes without the need to take off anything, pants over other pants, windpants over those pants. I think silk has been replaced by synthetics and merino wool as the best, whereas 10+ years ago it was #1,

Adam Keller, do you have any specific brands or garments of Merino wool you would recommend?

I currently own and wear Ice Breaker, Patagonia, and Helly Hansen merino wool base layers. I buy them when they're on sale, and they last for years. The extra price is definitely worth the quality and performance.