Generally, there are two types of paint brushes: those made of natural-hair bristles and those made with synthetic materials (usually nylon or polyester). Natural bristle brushes are preferred for use with solvent-based (oil- or alkyd-based) paints, especially for enamel or finish work. Natural bristles are hollow and can absorb the water contained in a latex paint, causing them to swell and become soft and limp (like your own hair when it’s wet).

Most synthetic brushes work well with both latex and solvent-based paints, but always check the manufacturer's recommendations on the brush. Some of the solvents used in solvent-based paints can break down the composition of a synthetic bristle. Once again, check the label.