I have been wearing merino wool briefs similar to these and also tee-shirts since discovering the Icebreaker brand when in New Zealand about 10 years ago.  Wool underwear (top and bottom) really is great in the is light in weight and feels soft on the skin.  It is comfortable year round (which suppose is why sheep sport), with an advantage over other fabrics is that it will keep you warm when it is wet.  These brief are prices at 25-30 percent less than Icebreaker and seem to be quite comparable.  I've found the Icebreaker to be quite durable (though do need to protect it from moths) and hope that this product is, though seems like some reviewers here have had issues.

Recommended.