The Merino is historically one of the most economically important breeds of sheep in the world, prized for its very fine and soft fleece. They were instrumental in the establishment of Spain as a world power through the 15th and 16th centuries, which held a monopoly over the trade of Merino fiber; today the Merino trade is largely focused in New Zealand and Australia, where many of the sheep were exported in the aftermath of the Napoleonic Wars.
The wool from these sheep is famed for its softness and fineness, with staples typically 65–100 mm long and a fiber diameter of less than 24 microns. The finest Merino yarn - usually marketed as 'ultrafine' - is suitable for blending with silk and cashmere.
The unique crimp of Merino also lends it interesting properties, helping to insulate against temperature extremes as well as transporting moisture away from skin. You won't get soaked in the rain as quickly as you would while wearing synthetic fiber garments and also won't get clammy with sweat to the extent that you would wearing synthetic fibers during a workout or enjoying the outdoors on a hot summer day.