Spending a week or two in a bush camp in cold weather means you are going to be living in your unwashed underwear and without a shower longer than you would normally consider doing. Nothing works as well as marino wool undergarments and shirts in those conditions. Synthetics are Ok for a couple ays, then they'll smell so bad you won't be able to stand your aroma. Smartwool, Icebreaker, etc. are worth the extra money they cost IMHO. I've done a couple of very long distance backpacking trips in the last 3 years, and have become a true believer in merino wool based on those experiences.
