Wicker is actually a weave type and process and not actually a type of furniture as most people think. The main material used for making patio and outdoor wicker furniture is Rattan. It is one of the oldest natural and most durable materials used to make indoor and outdoor furniture.
Rattan is a woody vine that grows in the tropical rain forests of Indonesia and South East Asia. Unlike bamboo which is hollow, Rattan is solid. The beginning process is to steam the Rattan and put it into whatever desired shape or form and let it cool. When cool it stays in that shape.
Generally Wicker outdoor patio furniture will have an aluminum frame for durability. Where steel frames are heavier and will rust, aluminum is lightweight and won't rust. The majority of the material is woven onto the aluminum and wicker pole frame. Because it is actually woven, wicker furniture usually carries a higher price than most other types of outdoor and patio furniture.