Fibrous soft tissues are ubiquitous in the human body. Skin, tendons, ligaments and arteries are all well-known examples. In mechanical testing, these soft tissues demonstrate nonlinear, anisotropic behaviour. The most mechanically relevant constituent of fibrous soft tissues is a strong protein called collagen, and the heterogeneous arrangement of collagen in soft tissues confers anisotropy. Nonlinearity arises as collagen fibres are crimped (i.e. wavy) in undeformed soft tissues and straighten as the tissue is deformed. In this talk, therefore, we shall propose a new strain energy function that assumes collagen fibres possess a triangular distribution of crimp. We shall fit the model to four existing stress-strain data sets of uniaxial stretching of mammalian skin, and compare the fits to those of two pre-existing models.