As a long time user of natural bristle brushes, I had my reservations about synthetic hair brushes. After trying the Catalyst brushes, I am a convert. When using these brushes, I immediately noticed that they kept their shape while painting, allowing for greater control. These synthetic brush hairs mimic the hairs of natural bristle, but have much greater strength. I can be very hard on brushes with my painting techniques and Catalyst hold much better than natural bristle brushes. The Princeton flats and filberts have long fibers which add greater flexibility to the brushes. The rounds really hold their shape, allowing for greater control of details and mark-making. If you are painting in heavy body acrylics, the Catalyst brushes are great because these brushes keep their properties in water, unlike natural bristles. These brushes are very easy to clean whether you are using oil or acrylic.