resins - solid or semi-solid materials, light yellow to dark brown, composed of carbon, hydrogen, and oxygen. Resins occur naturally in plants, and are common in pines and firs, often appearing as globules on the bark. Synthetic resins, such as polystyrene, polyesters, and acrylics (see acrylic resin), are derived primarily from petroleum. Resins are widely used in the manufacture of inks, lacquers, varnishes, plastics, adhesives, and rubber. See plastisols and organosols.