A quick definition...wool fibers are laid out, wetted down and pressed together. The fibers entangle and then are shrunk (fulled) about 1/3-1/2 by repeated throwing or rigorous rubbing. (See my earlier blogs for an extended definition).
Sheep are not the only animal fibers that felt. Fibers from alpaca, llama, camels, goats (mohair) and rabbit (angora) also make beautiful felted items. Sheep are shorn once a year. This wool is called a fleece. It does not kill the animal, however, I understand vegans do not use wool products because man is interfering with an animal’s natural process. If left alone sheep’s wool will fall off in clumps.
Below is a sample of Nuno felting with (top row) recycle cotton skirt pieces. The middle row is the china silk. If you look closely you can see the fiber coming through the silk with obvious folds in the fabric. The bottom has recycled silk chiffon pieces.