Wool. False-colour scanning electron micrograph of a sample of untreated wool from a Herdwick sheep. Two types of hair are visible; thin, solid (normal) hairs and thicker, hollow, insulating hairs. The broken end of one of the thick hairs reveals its internal honeycomb structure; it is filled with air pockets and forms an excellent insulating material for both sheep and man. Magnification: x40 at 35mm size.