Merino wool is common in high-end, performance athletic wear. Typically meant for use running, hiking, skiing, mountain climbing, cycling, and in other types of outdoor aerobic exercise, these clothes command a premium over synthetic fabrics.
Several properties contribute to merino's popularity for exercise clothing, compared to wool in general and to other types of fabric.
Merino is excellent at regulating body temperature, especially when worn against the skin.
The wool provides some warmth, without overheating the wearer. It draws moisture (sweat) away from the skin, a phenomenon known as wicking.
The fabric is slightly moisture repellent (keratin fibers are hydrophobic at one end and hydrophilic at the other), allowing the user to avoid the feeling of wetness.
Like cotton, wool absorbs water (up to 1/3 its weight), but, unlike cotton, wool retains warmth when wet helping wearers avoid hypothermia after strenuous workouts (climbs) or weather events.
Like most wools, merino contains lanolin which has antibacterial properties.
Merino is one of the softest types of wool available, due to finer fibers and smaller scales.
Merino has an excellent warmth-to-weight ratio compared to other wools, in part because the smaller fibers have microscopic cortices of dead air, trapping body heat similar to the way a sleeping bag warms its occupant.