Cutin is one of two waxy polymers that are the main components of the plant cuticle, which covers all aerial surfaces of plants, the other being cutan. It is an insoluble substance with waterproof quality and consists of omega hydroxy acids and their derivatives, which are interlinked via ester bonds, forming a polyester polymer of indeterminate size. Cutin also harbors cuticular waxes, which assist in cuticle structure. The C16 and C18 families are the two major monomer families of cutin. The C16 family consists mainly of 16-hydroxy palmitic acid and 9,16- or 10,16-dihydroxypalmitic acid. The C18 family consists mainly of 18-hydroxy oleic acid, 9,10-epoxy-18-hydroxy stearic acid, and 9,10,18-trihydroxystearate.

Cutin is especially noticeable on leaves and fruits of higher plants, where it plays an important role in waterproofing. It is a waxy, water-repellent substance allied to suberin, which is found in the cell walls of corky tissue. Cutin and waxes are fatty substances deposited in the walls of epidermal cells, forming a waterproof outer layer called the cuticle. The cuticle reduces the wettability of leaves and stems, thereby affecting the water balance of the plant. In desert plants, the cuticle is present as a thick waxy coating of cutin, which helps to reduce water loss through transpiration.