Contrary to popular belief, the fleece fabric on a warm, cuddly hoodie does not come from a warm, cuddly sheep. Traditionally, it's a 100 percent synthetic material that is derived from plastic, and can even be made from recycled plastic convenience items. Sometimes, however, it can incorporate natural fibers.

Traditional fleece fabric comes from polyester, which is made from plastic. The polyester is woven into a light fabric, which is then brushed to achieve greater volume in the fibers. It was invented in the late 1970s by engineers working for textile maker Malden Mills. The term "fleece" can also refer to the wool from one sheep, but this is not the same as fleece fabric; fleece fabric was actually invented to imitate wool.

Sometimes, however, fleece fabric can incorporate other fibers such as cotton, wool or rayon. Hemp fleece, for example, is a blend of hemp and other natural fibers. Fleece may incorporate other fibers to create a certain texture or to make colored ink designs more or less vibrant.

Fleece can also be made out of recycled plastic bottles, or already-existing fleece. In fact, traditional fleece is generally composed of polyethylene terephthalate, or PET, the same plastic used to make bottles for soda. The PET gives fleece its durability.