Leaf mold is a form of compost produced by the breakdown of shrub and tree leaves. Due to the slow decaying nature of their lignin (cellulose) content, autumn leaves break down far more slowly than most other compost ingredients, and therefore should be composted separately. This can be achieved either by placing the collected leaves in plastic bags (taking care to avoid collecting from areas that may be subject to high levels of pollution, e.g., roadsides), or in specially-constructed wire bins. To accelerate the breakdown process it is advisable to keep the leaves wet and avoid the drying effects of wind. The traditional wire enclosure may slow down the process by allowing the contents to dry out unless it is lined with cardboard or similar material.