Hog, boar, and pig hairs are called bristles because of their stiff and coarse appearance. They are actually so stiff that they were used as the balance spring in the first pocket watch. Bristle has a relatively uniform body with natural curve and a “flagged,” or split end. The curve is either removed or reduced during the boiling and preparation of the bristles. Interlocked brushes are made from hairs that have been boiled for only two hours so that some curve remains. An interlocked brush takes advantage of the curve; the bristles are assembled so that the curved bristles oppose one another. As with a broom, this helps keep the tip from splaying to give better control.
One of the desirable characteristics of hog bristle is flagging-the multiple tips provided by split ends. The greater the flagging, the better the control. Wild hogs have more split ends than the domesticated animal. Currently, the best hog bristle comes from China, where there are more wild hogs. Bristle from the Chungking province of China is said to be the best.