The Filbert brush is primarily used in artwork. It has a thick ferrule with hairs that are medium to long, in the shape of an oval. Filberts are particularly effective for blending, usually of a figurative nature. These brushes are ideal for soft floral painting, figurative work, and blending paints. They are great for use with acrylics, watercolors or tempera paints.
The Filbert brush, sometimes referred to as a Cat's Tongue, has a round outer edge. The Filbert's shape can vary from a flatter brush with a rounded outer edge, to an almost oval shape, to more of the Cat's Tongue shape that comes to somewhat of a point, for more control. Filbert brushes are sometimes considered a more advanced artist brush because it can take the place of Flats or Rounds depending on how the brush is held. You can blend broad strokes into fine strokes by turning the brush as you paint. This of course takes more control but has the advantage of not having to switch brushes as often.