Glossary

Undercoat

The soft, fine, dense layer of fur closest to a cat's skin that provides most of its insulation.

Also called: down hair, down coat, underfur

The undercoat is the layer of short, fine, wavy hairs that grow closest to a cat's skin. Sometimes called down hair or underfur, it traps a layer of air that holds in body heat. Cats with a heavy undercoat feel plush and cope well with cold weather.

The amount varies a great deal. Some breeds have a thick undercoat, others have very little. The Cornish Rex has almost nothing but down hairs, which is why its coat is so soft and wavy, while hairless breeds have little or none. Shorthaired indoor cats can have a modest undercoat that is hardly noticeable.

Undercoat is the part that sheds most and mats most easily. Fur that is not removed by brushing tangles into felt-like clumps close to the skin, especially behind the ears, under the legs and along the belly, where it can pull and hurt. Brush with a comb that reaches the skin, work gently, and cut nothing near the skin yourself, because the skin is thin and easy to nick. If you find a mat you cannot tease out, ask a groomer or your vet to remove it.

Last reviewed November 7, 2026

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Related terms

Double coat A coat made of a soft insulating undercoat beneath longer, coarser guard hairs, found in many cold-climate and semi-longhair breeds. Guard hairs The long, coarse outer hairs of a cat's coat that shed water and dirt and carry its colour and pattern. Ruff A collar of longer fur around a cat's neck and chest, most obvious in breeds such as the Maine Coon and Norwegian Forest Cat. Britches The long, full fur on the backs of a longhaired cat's hind legs, which forms a pair of fluffy trousers.

Related guides

Living with cat allergies What causes cat allergy, why no breed is allergen free, how to reduce exposure at home, and when to see a doctor. How to brush a cat How to choose a brush, groom short and long coats, handle mats and shedding, and make brushing something your cat accepts or enjoys. Keeping a cat warm in cold weather How to keep indoor and outdoor cats warm in winter, the winter hazards to watch for, and the signs of cold stress that need a vet.