It is the thickness of the wool fiber that determines whether wool is itchy or not. This is measured in microns, and the "limit for itching" for wool is 27 microns.
Standard Norwegian wool has a thickness of around 28 microns and upwards. This makes the Norwegian wool very durable, and it is sought after as furniture fabric and for carpets. However, because it is above the itch limit, it can itch if worn directly on the body, and most people use these types of wool cardigans and knitted sweaters as a second layer.
All merino wool garments from Pierre Robert are made from "fine merino wool" of 19.5 micron. This is far below the itch limit of 27 microns and feels soft and non-itchy against the skin. "Fine merino" is, however, above the "ultra-fine merino" category, which has a thickness of 14.5 microns and below. To achieve this wool quality, the sheep must be covered and kept in stalls, without being allowed to move freely in outdoor areas. The conditions in the production of ultra-fine merino wool are not according to the Pierre Robert Group's standards for good animal welfare.
How much wool itches also depends on where on the body the wool garment is to be used, and most people have a higher tolerance for itchiness on the feet. Many of our socks are therefore made in a wool blend with thicker wool than 19.5 micron merino wool.