Linseed oil, also known as flaxseed oil, is a colorless to yellowish oil obtained from the dried ripe seeds of the flax plant (Linum usitatissimum, Linaceae). The oil is obtained by pressing, sometimes followed by solvent extraction. Due to its high levels of α-Linolenic acid (a particular form of Omega-3 fatty acid), it is used as a nutritional supplement.
Linseed oil is a "drying oil", as it can polymerize into a solid form. Due to its polymer-forming properties, linseed oil is used on its own or blended with other oils, resins, and solvents as an impregnator and varnish in wood finishing, as a pigment binder in oil paints, as a plasticizer and hardener in putty and in the manufacture of linoleum. The use of linseed oil has declined over the past several decades with the increased use of synthetic alkyd resins, which function similarly but resist yellowing.