Hate making decisions? Well, lucky for you there are only two types of composite decking on the market: solid and hollow. Solid looks more like wood and is heavier than the hollow version. Because of its greater mass, solid decking will expand and contract more with temperature fluctuations.
Hollow composite decking has a more man-made look. However, it won't expand and contract as much as solid composite decking. You need to be careful when handling it, though, because it's more susceptible to damage before it's installed. Solid composite decking is more popular because of its superior strength and closer resemblance to real wood [source: Montenegro].
Regardless of the type of composite decking, it's important that the product is treated with a preservative and antifungal chemical. When left untreated and exposed to the elements, most wood will rot over time. Excessive moisture accelerates the rotting process. Even though the wood fibers and other cellulose in the decking have been combined with plastic, it can still rot, according to the Forest Products Journal. Considering that most composite decking products consist of at least 40 percent wood (sometimes as much as 70 percent), the lack of a preservative could cause serious problems. And some composites have wood contents as high as 70 percent [source: Carter].
The preservative is mixed in with the wood during the manufacturing process. Some preservatives, like zinc borate, can remain active in composite decking for more than 20 years.