Traditionally, bows are made from pernambuco or brazilwood. Both come from the same species of tree (Caesalpina echinata), but pernambuco, used for higher-quality bows, is the heartwood of the tree and is darker in color than brazilwood (which is sometimes stained to compensate). Pernambuco is a heavy, resinous wood with great elasticity which makes it an ideal wood for instrument bows.
Bow sticks are also made from carbon-fiber, which is stronger than wood. Inexpensive, low-quality student bows are often made from fiberglass. An average cello bow is 73 cm long (shorter than a violin or viola bow) 3 cm high (from the frog to the stick) and 1.5 cm wide. The frog of a cello bow typically has a rounded corner like that of a viola bow, but is wider. A cello bow is roughly 10 grams heavier than a viola bow, which in turn is roughly 10 g heavier than a violin bow.
The bow hair is horsehair, though synthetic hair in different colors is also available. The hair is coated with rosin by the player to make it grip the strings and cause them to vibrate. Bows need to be re-haired periodically, especially if the hairs break frequently or lose their gripping quality. The hair is kept under tension while playing by a screw which pulls the frog (the part of the bow under the hand) back.
