In biology, an indumentum (Latin, literally: "garment") is a covering of trichomes (fine "hairs") on a plant or of bristles (rarely scales) of an insect.

The indumentum on plants can have a wide variety of functions, including as anchorage in climbing plants (e.g., Galium aparine), in transpiration control, in water absorption (Tillandsia), the reflection of solar radiation, increasing water-repellency (e.g., in the aquatic fern Salvinia), in protection against insect predation, and in the trapping of insects (Drosera, Nepenthes, Stylosanthes). Plant indumentum types include

The use of an indumentum on insects can be pollen-related as on bees, sensory like whiskers, or for other uses including adhesion and poison.