Bristles may be natural or synthetic. If the filaments are synthetic, they may be made of polyester, nylon or a blend of nylon and polyester. Filaments can be hollow or solid and can be tapered or untapered. Brushes with tapered filaments give a smoother finish.
Synthetic filaments last longer than natural bristles. Natural bristles are preferred for oil-based paints and varnishes, while synthetic brushes are better for water-based paints as the bristles do not expand when wetted.
A decorator judges the quality of a brush based on several factors: filament retention, paint pickup, steadiness of paint release, brush marks, drag and precision painting. A chiseled brush permits the painter to cut into tighter corners and paint more precisely.