Wool is a natural fiber, shorn primarily from sheep as well as goats and llamas. The fiber has long been used to create warm and durable clothing and blankets. Modern uses of wool extend beyond winter attire, as wool can be found in carpeting, insulation, felt and luxury suits used in many different applications. Wool is different than fur: it has characteristic bends, or crimps, along the fiber, has the capacity to stretch when woven and grows in clusters known as staples. The crimps let the fibers bunch together, which results in a bulkier material that also acts as a superior insulator. Fine wool, such as Merino, may have dozens of crimps per inch, while rougher wools may only have a handful. Wool fabric has the unique ability to stretch much further than silk, cotton, or other natural fibers and regains its original shape after being stretched. It has an extremely high absorbency rate and is flame retardant, which makes it useful in firefighters' uniforms and carpeting in trains and airplanes. Wool is resistant to static electricity; the fabric will not cling to the body or produce a spark. The use of wool car seat covers or carpets reduces the risk of a shock when a person touches a grounded object. Wool is naturally absorbent, and can absorb almost 1/3 of its own weight. Wool is considered by the medical profession to be hypoallergenic.