A paint brush's performance depends upon the bristles. A quality brush will have solid filaments as opposed to hollow filaments. Bend a filament at the base—solid ones spring back, while hollow ones won't. Densely packed bristles that taper to a chisel edge help with painting a straight edge, cutting in, or tipping. Split ends or flags hold more paint and spread it more evenly and smoothly. Here's a quick run-down of the different types of paint brushes and their uses.
Natural vs. Synthetic Bristles
Paint brushes with natural bristles are meant for oil-based paints. The newer synthetic bristles can be used for anything, but were really designed for water-based paints. Natural bristles will soak up the water and go limp in water-based paints.
Badger or Ox hair Bristle
Badger hair brushes feature the softest natural bristles. They're best for creating glass-smooth finishes with oil enamels and varnishes.
White China Bristle
For oil-based paint, stain, varnish, and polyurethane, as well as shellac and lacquer, we recommend using a paint brush that features white china bristles. Soft natural bristles yield a smoother finish than a black china bristle.
Black China Bristle
These brushes are best for oil-based paint, stain, and varnish. Their bristles are stiffer and may require a more forceful stroke to get the paint onto the surface. Black china bristle brushes are the least expensive natural bristle brushes.