Before you purchase your next carpet, there are a few things you should know. First, the density of the carpet has a lot to do with how long it will last. A good rule of thumb is that if you can see the backing through the fibers, the carpet won't last as long.
Dense carpets have finer fibers, which displace weight over more material.
A better carpet won't look much different from a low-density one until a few years have gone by and the cheaper carpet has begun to wear out. The kind of fiber your carpet is made of also affects its durability. Polypropylene carpets offer more stain resistance but are less durable. Polyester carpets offer some stain resistance and better durability. Nylon carpets are very durable but don't have the stain resistance of polypropylene and polyester.