Do they make you itch? Especially if you start sweating a little.
Regular wool has microscopic barbs on the fibers that cause the itch. Merino wool has far fewer of them so itch is greatly reduced. Those barbs are also what makes wool so susceptible to shrinking when washed. The barbs lock together and won't come apart. That pulls the fibers closer together and makes the garment smaller. I've washed and dried my merino shirts many times with no shrinkage at all.
