Most residential carpet is manufactured using a process known as tufting.  Tufting, a process of inserting pile yarns into a backing material, accounts for more than 90% of the carpet produced today.  This process revolutionized the manufacture of carpet by speeding production and making carpet more affordable for the masses.

Tufting is a process very similar to embroidery. Yarn is inserted into a backing material to form the face material.  In fact, tufting originated from the manufacture of embroidered chenille bedspreads and was gradually transformed into rugs and later broadloom carpet.

Once a tufted blanket has been stitched (yarns inserted into a primary backing material), the blanket is back coated with a synthetic latex adhesive to lock the fibers in place. A secondary backing is then applied to provide dimensional stability. (See diagram).

Modern tufting involves  Modern Tufting involves high-speed machines with numerous “stitching” (tufting) needles lined side by side across the width of the carpet. Visualize a sewing machine with 1400 needles. The distance between these tufting needles, known as gauge rate, helps determine the density of the face.  Residential carpet is  ³/₁₆, and ³/₈ gauge. Gauge is measured in needles per inch across the  width.  

The following diagram describes the number of needles per inch for each gauge rate and the number of tufts across the 12-foot width of carpet.

The number of tufts along the length of carpet is known as stitch rate.  Stitch rate, in combination with gauge rate and yarn pile height, is a primary factor in determining product density and thus product performance.  Stitch rate is measured in stitches per inch along the length of the carpet.  Stitch rate is easily varied during manufacturing so stitch rate may vary more than gauge rate.  Gauge rate is limited by the preset positioning of the needles on a particular machine; whereas stitch may be changed.  In other words, an ¹/₈^th-gauge machine will always manufacture ¹/₈-gauge products, but may tuft a variety of stitch rates.  Ideally, stitch rate should represent a similar construction to gauge rate.  A ¹/₁₀- gauge fabric should have a stitch rate of around 10 stitches per inch.

Pile height, the third component of carpet density, is measured from the surface of the primary backing to the top of the tufted yarn.  The higher the pile height, the lower the anticipated performance.  For example, an ¹/₈^th-gauge product with 8 stitches per inch with a ¼- inch pile height will outperform an ¹/₈^th-gauge product with 8 stitches per inch with a ½ -inch pile height.  In this instance, the lower pile height provides a higher density construction and better performance.

Twist level, is rarely examined by consumers or retail salespeople with regard to performance, but twist level can have an enormous impact on performance.  Products with higher twist levels have the tendency to hold their original appearance longer than lower twist products.  Lower twist products tend to untwist or “blossom” at the yarn tips creating a trafficked appearance.  This characteristic provides the “wet poodle” appearance associated with many residential constructions.  As the yarn tips untwist, they begin to intermingle with other yarn tips and a matted appearance is displayed.

Twist level is measured in turns per inch.  Many frieze products may have 7 to 9 turns per inch, while lesser quality saxonies may have only 3 to 4 turns per inch.

Each of these three dimensions contributes to the anticipated performance of the carpet selected.  The higher the density of the construction, the better the performance. Determining each of these factors is as easy as taking along a ruler to measure each of the dimensions.  Keep in mind that few products offer the best of each of these factors.  Each factor contributes to the cost of the product as well. Also, a product of the finest quality that displays each of these attributes has a much lower perceived value in the consumer’s eyes. A densely constructed product with a high twist level may exceed your individual budget and may not provide the softness, cushion, hand, or look that you desire.

Carpet Density

With each of these construction characteristics in mind, several formulas are available to evaluate carpet density and forecast performance.  These three formulas include: Average pile yarn density, weight density, and pile density index.  Finally, there is a Canadian formula for Pile Density as well.

Average Carpet Pile Yarn Density -   This formula is commonly used among carpet specifiers and by many carpet retailers.

    36 X w

    t (Or T)    36 times pile yarn weight divided by tuft height (cut pile) or pile thickness

Where:    

            w =  pile yarn weight in ounces per square yard

            t = pile thickness for loop piles (ASTM D-418)

            T = tuft height for cut piles (ASTM D-418)

A 30 ounce cut pile with 1/2 inch pile height (36 X 30 = 1080 ÷ .50 = 2160)

A 30 ounce cut pile with 1/4 inch pile height (36 X 30 = 1080 ÷ .25 = 4320)

In this instance, the second carpet with the lower pile height has a higher density as you might expect.

Weight Density - This formula places a higher relevance on pile yarn weight

36 x w²

 ^{t (or T)     36 times weight times weight divided by pile height (cut pile) or pile thickness}

A 30 ounce cut pile with 1/2 inch pile height (36 x 30 x 30 = 32400 ÷ .50 = 64800

A 30 ounce cut pile with 1/4 inch pile height (36 x 30 x 30 = 32400 ÷ .50 = 129600

Pile Density Index -  This formula utilizes stitch rate and gauge rate and disregards pile height altogether.

Yarn denier times rows/inch time stitches /inch

An 1/8 gauge product with 6.5 stitches per inch using 2600 denier would have a pile Density index of 135200

2600 times 6.5 times 8 (gauge)

Whereas

a 1/10 gauge product with 6.5 stitches per inch using 2600 denier would have a pile density of  169000

2600 times 6.5 times 10 (gauge) = 169,000

The Canadian method and we list this for Canadians only.

yarn tex number X tufts/100cm²

              100000 

           or

yarn denier X pile ends/sq. inch

           58070

The Canadian method is similar to the pile density Index except the conversions are performed in metric values.

An 1/8 gauge product with 9.5 stitches per inch made with 2300 denier has a calculated pile density of 6.02 ktex/cm² ( To obtain pile ends per square inch, double the tufts per square inch)--Canadians can figure this out though.

It will pay dividends to be aware of these characteristics when shopping for new carpet, but you must be flexible in shopping for the perfect product.  Other factors, including fiber type, dye method, color, stain treatments, and carpet cushion (carpet padding) .