They are rigid and balanced along a vertical axis. Human proportions are treated freely with greatest emphasis on the head. Most are images of gods, spirits, or ancestors, where realistic details are irrelevant. Icons therefore don't try to imitate observable realities, but reflect order, immutability and inner realities. The individual forms and shapes are dictated by individual cultures.
Materials play an important role in African works.
Most have symbolic qualities, e.g. wood may come from trees inhabited by spirits, therefore masks and figures from this wood have spiritual dimensions. Wood is the dominant material. Most African tribes recognize both male and female woods, and appropriate works are made from each. Male woods, like oak, are hard, strong, and resistant to insects. They are used when durability is required.