With their corresponding properties, Hirano classifies the layers of the vocal folds into five minute layers (as cited in Altman, n.d.). The outer protective layer is the squamos epithelium, which is responsible for sustaining the form of the vocal fold and its hydration. The next layer is the superficial lamina propia (SLP) which is composed of loose fibrous and elastic components that possess mechanical properties due to its cushion-like assets. The intermediate lamina propia (ILP) on the other hand, is generally composed of elastic fibers, which therefore adds to the elasticity of the vocal folds. Then there is the deep lamina propia (DLP), the vocal fold layer that consists of collagenous fibers that is responsible for the durability of the vocal fold. The fifth layer is the vocalis muscle. It as a muscle and therefore has active (contractile) properties that helps in controlling the stiffness of the vocal folds when it is vibrating, contracting or at rest. These layers vary in terms of stiffness and therefore were grouped further accordingly. The cover layer or mucosa is composed of epithelium and SLP, while the vocal ligament is composed of the ILP and DLP.