The spælsau sheep (ovis aries) is one of the Northern European short-tailed sheep breeds. It is well adapted to the Nordic climate and was a domestic animal from the Iron Age. The wool is characterized through having two layers. The outer long-haired layer of wool is protecting the underlying layer against rain and wind. The underlying layer keeps the sheep warm. Its use in Norway goes at least as far back as the Viking age (from 800 to 1066 AD), where a dense fabric used as clothes allowed survival in North Sea weather. The Viking ship sails were also made from spælsau yarn. Spælsau wool can be a bit rougher than wools that are popular today, but it is exceptionally strong, and can protect against wind and rain, and it makes a traditional Nordic sweater that is truly authentic.