A filbert, No. 12, artist's paintbrush with synthetic fibres made from polybutylene terephthalate (PBT). A filbert brush is a combination of a flat, rectangular brush with a rounded end so it can create a variety of marks and is particularly effective in blending. Sable, mongoose and badger hair can all be used effectively in this type of brush because they are soft, but the Procryl range is a vegan alternative from Jackson's, for use with oils and acrylics. Using filament manipulation technology to provide a blend of 'dull' and 'shiny' fibres, the resulting brush is responsive, absorbent, with a good spring and point retention. The Procryl paintbrush also uses 'crimped' fibres that possess a wave in the filament so that they flare out more at the tip, further enhancing the softness. The synthetic fibres have been dyed to resemble the colour variation seen in natural hair.