Crafted from pure New Zealand Merino wool, Icebreaker makes the finest base layers I have used. Yes, I said “crafted”. The material is heaven and Merino naturally repels odors as well as being inherently FR. Additionally, it is breathable and like all wools insulates even when wet.
My favorite piece is the Boxer Brief. They are so comfortable that you can wear them all year round (preferably not the same pair). In addition to base layers they have also introduced mid and outer layers as well. Check them out.
Available in a variety of colors, they can be purchased here or from many fine outdoor retailers.