Have you ever knitted with Icelandic wool? It is quite the experience. Elizabeth Zimmerman and her daughter Meg Swanson have several patterns that feature this warm fiber.
What is it exactly? Well, Icelandic wool is the long fibers from Icelandic sheep. The fiber is not spun. Instead is it carded into very thin roving. The roving is then put into skeins that are called "bobbins."
If you use it single stranded it equals a DK weight. If you use it doubled it equals a nice worsted weight. It also blooms really well.
I am knitting a rectangular lace shawl for myself. I am using it doubled and love it!