Brushes
Brushes are categorized by the material used in the bristles.
Natural-bristle brushes, made from boar's hair, should be used only when applying oil-base paints. Their natural oils let paint flow out smoothly. If you use a natural-bristle brush with a latex paint, the bristles, which are hollow, will soak up a large amount of the water in the paint and will quickly become limp and unmanageable.
Synthetic-bristle brushes, made from nylon, polyester, or a nylon-polyester mix, can be used to apply all latex paints, and many can also be used with alkyd coatings. Nylon will retain its shape longer when you're faced with a large paint job requiring latex paint. Some synthetic brushes have hollow bristles; they are made solely for the application of oil-base paints, not latex.
Paintbrushes have more jobs to do than simply get the paint on the wall. The best brushes will do these things:
-- give you the best paint pickup (paint loads quickly and evenly)
-- provide the best transfer (put as much paint on the wall with one stroke as possible, and do it smoothly)
-- level effortlessly (leave a smooth film without brush marks)
-- cut in sharply (create a sharp straight paint line)
Quality brushes have split or flagged ends that are flexible, qualities which help produce a smoother finish. The bristles are tapered, with those in the center slightly longer than those at the edge. There should be a divider at the heel of the bristles to provide a reservoir for the paint. Quality brushes feature bristles at least half as long as they are wide (for example, the bristles on a 2-inch-wide brush should be at least 3 inches long).
A bare wood handle, rather than plastic or painted wood, will give you a better, more comfortable grip (which you'll be grateful for after cutting in the edges of a wall for an hour). A quality brush should be bound with a rust-resistant metal ferrule that is nailed on, not just crimped to the handle.
You can get by with just one brush when painting, but a collection of several sizes will serve you better. A 4-inch brush with bristles 3/4 to 1 inch thick is good for general exterior painting; a 3-inch brush will do for most interior painting. Use a 2-inch brush to cut in corners for interior work. And get a 1- to 2 1/2-inch angled sash brush for interior and exterior trim, window frames, and moldings.