Carpet looks like a single soft surface, but it is assembled from four distinct components, and each one affects how it performs. At the top is the pile, the visible fibers you walk on. Those fibers are anchored into a primary backing, a woven or non woven sheet that holds them in position. A layer of adhesive is applied beneath that to lock the fibers permanently in place. Finally a secondary backing is bonded to the underside to give the whole thing dimensional stability and body. Separately from the carpet itself sits the cushion or pad, which is not part of the carpet but has as much influence on how it feels and how long it lasts as anything in the construction above it.
The overwhelming majority of carpet made today uses one of four fibers. Nylon is the most durable and the most resilient, meaning it recovers its shape after being compressed by furniture or footfall, which is why it dominates commercial specification and high traffic residential areas. Polyester is softer to the touch and takes color exceptionally well, producing rich deep shades, but it is less resilient and tends to flatten sooner under sustained traffic. Polypropylene, often sold as olefin, is highly stain resistant and inexpensive, though it is the least resilient of the group and shows crushing readily. Wool, the only natural fiber in common use, is durable, naturally flame resistant and recovers well, and it is priced accordingly. Each one is a genuine trade off rather than a simple hierarchy.
How the fibers are finished at the surface changes the carpet as much as what they are made of. In loop pile, the yarn is left as continuous uncut loops, producing a dense, hard wearing surface that hides traffic patterns well, which is why it is the standard in offices and corridors. Berber is the familiar name for a loop construction with a chunky appearance. In cut pile, those loops are sheared open so the yarn ends stand upright, which is softer underfoot and gives a more luxurious appearance. Within cut pile there are further variations, saxony with its smooth even surface, frieze with tightly twisted fibers that curl and disguise footprints, and plush with a velvet like finish that shows every mark. Cut and loop constructions combine both in the same carpet to create patterns and texture.
Three specifications describe carpet quality, and they are more informative than the appearance of a sample. Face weight is the amount of fiber in a given area, measured in ounces per square yard, and a higher figure means more material. Density describes how tightly those fibers are packed together, which matters more than face weight alone because loosely spaced fibers bend and crush regardless of how much yarn is present. A practical test is to bend a sample backward, and the more backing you can see through the fibers, the less dense the carpet. Twist level describes how tightly each individual yarn is wound, and higher twist resists untwisting and fraying at the tips, which is what makes a carpet look worn long before the fibers themselves have gone.
The pad is bought separately, chosen almost as an afterthought, and it has a disproportionate effect on everything. It absorbs the impact of footfall that would otherwise be taken by the carpet fibers, which extends the life of the carpet considerably. It provides the softness underfoot that most people attribute to the carpet itself. It adds insulation and absorbs sound. Pads are specified by thickness and by density, and density is the more important of the two, because a thick soft pad allows the carpet to flex excessively and actually shortens its life rather than extending it. Most carpet manufacturers specify a maximum pad thickness in their warranty terms for precisely that reason, and installing something thicker than specified can void the coverage on the carpet above it.
