Traditional natural wicker made from rattan, bamboo or seagrass is strong but does not fare well outdoors. It's susceptible to warping, mold and mildew from rain and humidity. In drier climates, it may become brittle and crack.
Almost all wicker used for patio furniture is now woven from polyethylene resin. This synthetic wicker is extremely dense, strong and weather-resistant. Additionally, it does not fade quickly so your outdoor seating and tables will last a long time. High-density polyethylene (HDPE) is the most durable resin wicker, while lower quality PVC wicker will degrade over a shorter period of time. The one thing to be careful about with synthetic wicker is that it is lightweight and may be damaged in windy conditions depending on the woven design.