Icelandic fibre is one of the primitive breeds. These are breeds that have not changed from cross-breeding over time. The fleece typically has an outercoat that sheds water and a downy undercoat that traps warmth. In the icelandic, the outer coat is called tog and the undercoat is thel.
Lopi yarn is traditionally spun from Icelandic fleece and are used to make the traditionaly lopi sweater.