There are 4 different factors you have to take into consideration when deciding on which paint brush is right for the job. First of all you have to decide what TYPE of brush you need. There are three different types of brushes Natural-bristle brushes, Blended nylon/polyester brushes and Polyester brushes. Natural-bristle brushes are made with animal hair and are generally used for applying oil based paints and oil based finishes. The natural splitting of the hairs at the end of the brush helps to hold more paint and help assure a smooth paint release and finish. Blended nylon/polyester brushes work best with latex paints and latex finishes. The durable fibers are easy to clean and built to handle numerous projects. Polyester brushes are also great to use with latex paints and latex finishes. Polyester brushes hold their shape and stiffness in any paint and apply paint smoothly and evenly. Next you need to consider what size brush you need for the job. Typically a 1″-2″ brushes are best used for window and other small trim, 3″ brushes are best used for glossy paints for doors and cabinets and 4″ and above brushes are best used for large flat areas. When choosing the best brush for the job you also have to consider brush end types. A chisel trim brush has slanted bristles which produce straight line for trimming in corners and edges. Square trim brushes have a square cut at the end of the bristles and used primarily for applying paint over flat areas. Angled brushes bristles that are cut to and angle at the end of the brush and are best used for trim work and any area that you need to cut. Last but not least you must choose the correct brush style to use. Thin angle sash style brush has its bristles slanted at the end and has a thin profile, they are best used for cutting trim in corners and edges. Angle sash style brush features slanted bristles and is slightly larger than the thin angle brush, they are great for cutting in at the ceiling or painting trim. Flat sash style brush has its bristles straight across and used primarily for applying paint over flat areas. Trim style brush is a flat brush that is great for painting large flat surfaces, especially exterior siding. Wall style brush is a thick flat brush that holds a large amount of paint, they are great for painting larger surface areas.