Princeton's Catalyst Polytip Bristle brushes are super stiff, but truly responsive. The advance in Catalyst is the Polytip feature: for the first time, the tip of each individual hair has been split to replicate the natural flags on the finest natural bristle. By giving each individual hair 2 to 3 distinct tips, Catalyst is able to hold a higher volume of paint while providing a smoother application. Designed for use with medium to heavy-bodied acrylics and oil paints.