Felted

Felted is a term variously applied to hairy or otherwise filamentous material that is densely packed or tangled, forming felt or felt-like structures. Apart from fibres in felted fabric manufactured by humans, the term "felted" may apply to the condition of hair such as in the pathological condition known as felted hair, or it may apply to the tangled threads of the tissue of certain fungi, to matted fibres in animal connective tissue, or to the felted outer coat of certain plants. To say that something is felted need not imply that any processes of matting, condensing and pressing fibres have been applied as in the processes for artificial production of felt fabric. Depending on the nature of the felted material, it might rely purely on the scaly or barbed texture of the matted fibres to prevent unraveling, but commonly it will include clayey or sticky materials for its structural integrity, or for increased density.

Examples of the description of animal tissues as "felted" include classes of connective tissue such as the dermis which the classic Gray's Anatomy describes as: "felted connective tissue, with a varying amount of elastic fibers and numerous bloodvessels, lymphatics, and nerves." Also, in describing the external coat or tunica adventitia of an artery, Gray says: "...consists mainly of fine and closely felted bundles of white connective tissue..." In such classes of connective tissue the felted structure is very important; it is versatile in resisting tearing by distributing localised stresses and it imparts strength together with shock absorption and elasticity in two or three dimensions at once, irrespective of the shape of the tissue. In other words, suitable types of felting can yield controllable isotropy or anisotropy in the behaviour of a structure.

Other examples of felted material in animal structures include fibrous structures coating the integument of some insects. Usually such a felted coating is not living tissue, but consists of waxy fibres and is not particularly strong, but serves as protection from either excessive desiccation or moisture. It is particularly common in some families of the Hemiptera. In some species it occurs only as an outer coat of the immature insect, but in others, such as many of the Coccoidea, including the "Australian bug", Icerya purchasi and cochineal, Dactylopius species, it is secreted throughout the life of the insect and serves largely to protect the eggs rather than the insect. In other species, such as many of the "woolly aphids", the Eriosomatinae, the most spectacular fluff is borne on the adult insect itself.

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