Hog bristle are natural fibers that are stiffer, more elastic and stronger than "soft hair" fibers. They are better suited to thicker, pastier paints, such as oils or acrylics, whereas water-based paints will make these fibers swell, altering the appearance of the brushstroke.
The fan shape, also known as a "blender" brush, is used to spread and blend paint over broad areas.
