NaturalNatural Brushes are used for oil-based paints. SyntheticFrogTape works best with latex or water-based paints which are best applied with synthetic brushes. These brushes keep their shape and maintain stiffness no matter how much water theyre exposed to. Then, choose a brush size and shape: Smaller, angled brush is for cutting and trim work. Flat brush is great for molding. Larger brushes are used for painting corners or when youre covering larger surfaces