The vast majority of rugs are tufted, hooked or hand-knotted, all of which result in a pile. Pile is a measure of the density of the fibers that comprise a rug, and pile height is determined by the measurement from the surface of the carpet to the backing. Only flat-woven rugs lack a pile, and these types of rugs are usually reversible.

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Carpet Construction Methods

With the exception of flat-woven rugs, carpet construction begins with a backing, which is a woven substrate of cotton or synthetic fibers. The actual carpet material is a yarn spun from wool, silk or a synthetic material, such as nylon, polyester or polypropylene. Modern carpet manufacturers usually tuft carpets by passing the yarn through the backing to form a series of continuous loops; whereas, traditional carpet-makers knot each loop individually. When the tufting process is complete, the carpet may then be sheared to cut the loops into individual strands, or it may be left as it is to give the rug an embroidered appearance. Hand-knotted rugs are seldom sheared.

Piling on the Snuggle Factor

Pile thickness is one way to measure the luxuriousness of a rug. The pile height on shag carpeting, the ultimate in coziness in rugs, may exceed 3/4 inches, whereas that of utilitarian indoor/outdoor carpeting can be as low as 1/4 inch. Long pile height has attractive characteristics, such as better sound- and heat-insulation properties and a very textured appearance, but it also has drawbacks. Carpets with a high pile are more difficult to keep clean, because dirt tends to get lost in the pile, and they are more susceptible to damage from moisture, spills and heavy traffic.

Keeping the Pile Low

Longer pile height may make for a more luxurious rug, but it doesn't produce a stronger one. Carpets with a low pile tend to last longer than their high-pile counterparts, and they are easier to vacuum and shampoo. Unlike shag rugs, low-pile fibers won't get caught in the beater bar of your floor vacuum and tear. In hand-knotted rugs, short and medium pile heights are often an indication of quality, because carpet-makers can fit more knots onto the carpet if the pile height is moderate or short.

Choosing Carpets for Pets

It may be heartwarming to watch your dog or cat snuggle into a shag rug, but the warm feelings may disappear when you have to clean it. Longer pile carpets, especially those with looped ends, aren't the best choices for a house with pets, especially dogs or cats that like to play in the yard. Their claws get caught in loops, and when they come inside after playing, they usually deposit part of the yard deep in the pile of the rug. Unless your pets are completely house-trained, you'll be doing them -- and yourself -- a favor by sticking to low-pile rugs.