The sub-layer of skin called the stratum spinosum is believed to aid in flexibility, and it enables the epidermis, or outer layer of skin, to better withstand the effects of friction and abrasion. The stratum spinosum is thicker in those areas of the skin, such as the soles of the feet and palms of the hands, that experience a greater degree of abrasion from contact with external surfaces. The thickness of the sub-layer in these areas appears to support its function in providing strength and flexibility.
The stratum spinosum is also called the "prickly layer" because of the spiky microfilament projections that are found in this sub-layer. These spine-like structures account for the "spinosum" portion of the skin layer's name and are believed to serve as the underlying structural reinforcements that provide strength, elasticity and flexibility to the outer layer of skin.