Proof that the Vikings made sails out of wool came with discovery of the Gokstad ship in 1879. The wool was from a special breed of sheep that had two layers, a coarse outer waterproof layer and a soft inner layer for insulation. These were separately spun and woven together, then coated with horse fat or fish oil and ochre to give a waterproof sealant. The Merino breed of sheep used in New Zealand are famous for the softness of their wool.
AKA A Thread to Your Heart