Most disposable items are made of plastic, a highly malleable substance but one which requires a great deal of energy to produce. In recent years, efforts to recycle plastic have intensified in some developed countries. Many people see this as an easy solution to the problem, one that will permit the continued unbridled consumption of plastic products. However, recycling plastic is not as simple as that. The first problem has to do with the collection and transport of the plastic. Plastic takes up almost twice as much space as other substances since 45 percent of a load of plastic actually comprises air. So the cost is high. Then there is the wide variety of types of plastic, one of its main advantages in the marketplace. This asset, however, becomes a major problem when it comes to separating the objects for recycling. Separation is a vital part of the recycling process, since each different chemical compound requires a different treatment. For example, two of the most common types of plastic are PET, used in soft drink bottles, and PVC, used for water and oil bottles. PET breaks down at a temperature at which PVC only begins to melt. This means that if a PVC bottle is accidentally put in with thousands of PET bottles being recycled, the whole procedure could be spoiled. The second major problem is that many of the properties of plastic are lost or degraded in the recycling process. For example, recycled garbage bags are not as durable as the originals, making them less valuable. It is no coincidence that PET, which can be used in a wide variety of products after being recycled (in everything from sleeping bags to bottles), comprises over a third of all plastics recycled, yet its percentage of total sales is no more than 5 percent. Other types of plastics such as HDPE, used in milk bottles or detergent containers, have been shown to absorb their contents, a problem that prevents them from being cleaned properly. That is why the US Food and Drug Administration does not permit the use of recycled plastic in food packaging. So, while recycling plastic might be a good idea, reducing the volume of these goods is even more vital.