Face-weight: Carpet is assigned a weight, from 25 to 70 ounces, based on the amount of yarn in a square yard. The higher the number, the more durable the carpeting. But the measure is only useful when comparing the same material. A polypropylene sample, for instance, may weigh more than a nylon one but won't perform as well.
BCF versus staple fiber: Carpeting is woven from either bulked continuous filament (BCF) yarn, created from long threads, or staple yarn, derived from shorter strands. Most synthetic carpets are made with BCF yarn, whereas wool is a natural staple fiber. Both are equally durable, but staple carpets will shed for a few weeks after installation.
Twist: The number of times a carpet fiber is twisted per inch of length. Most yarns have between 2½ and 8 turns; a tighter twist indicates a longer-wearing carpet. Manufacturers don't typically tout their twist numbers, so you may want to count for yourself.
Warranty: Quality carpeting should have a warranty of at least seven to 10 years. Pay special attention to the stain and texture-retention warranties. Stain warranties typically cover discoloration from food and beverages but may have exceptions for pet stains and spots caused by blood, grease, ink, and cosmetics. Texture-retention warranties cover fibers' ability to maintain their original shape for a specified length of time.