Collagen fibres. Coloured scanning electron micrograph (SEM) of bundles of collagen fibres from connective tissue. The characteristic banding pattern is seen on each individual fibre. The width of a collagen fibre can range from 1-12 micrometres (millionths of a metre) because it depends upon the number of smaller fibrils contained in the fibre, a number that varies depending upon the type of collagen. Collagen is the body's major structural protein, forming large bundles found in tissues such as bones, tendons and skin.