From humble beginnings more than 30 years ago as scrap byproducts of the carpet and steel wool industries, fibers today offer many advantages for reinforcing concrete. Today's market offers great variety, from short, hair-thin strands (micro- or monofilament) to macro-fibers up to about 2 inches long. Fibers are made of glass, carbon, steel, nylon, polypropylene, and other materials. They can be fibrillated (frayed) or smooth, crimped or flat, colored or transparent.