A pill, colloquially known as a bobble, is a small ball of fibres that forms on a piece of cloth from wear. Pill is also a verb for the formation of such balls.

All fabrics pill to some extent. With weaker fibres the pills fall off, but with stronger fibres the pills remain attached to the fabric. Whether a fabric pills or not depends both on the fibre and the preparation. Some fibres, such as cotton

Cotton

Cotton is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. The botanical purpose of cotton fiber is to aid in seed dispersal....

, acrylic

Acrylic fiber

Acrylic fibers are synthetic fibers made from a polymer with an average molecular weight of ~100,000, about 1900 monomer units. To be called acrylic in the U.S, the polymer must contain at least 85% acrylonitrile monomer. Typical comonomers are vinyl acetate or methyl acrylate...

 and wool

Wool

Wool is the textile fiber obtained from sheep and certain other animals, including cashmere from goats, mohair from goats, qiviut from muskoxen, vicuña, alpaca, camel from animals in the camel family, and angora from rabbits....

 have a high tendency to pill, whereas other fibres such as polyester

Polyester

Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...

, linen

Linen

Linen is a textile made from the fibers of the flax plant, Linum usitatissimum. Linen is labor-intensive to manufacture, but when it is made into garments, it is valued for its exceptional coolness and freshness in hot weather....

 and silk

Silk

Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...

 do not. In general longer fibres pill less than short ones because there are fewer ends of fibres, and because it is harder for the longer fibres to work themselves out of the cloth.

Techniques used to avoid pilling include singe

Singe

A singe is a slight scorching, burn or treatment with flame. This may be due to an accident, such as scorching one's hair when lighting a gas fire, or a deliberate method of treatment or removal of hair or other fibres.-Hairdressing:...

ing the loose fibres protruding on the surface of textile

Textile

A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

, and spinning

Spinning (textiles)

Spinning is a major industry. It is part of the textile manufacturing process where three types of fibre are converted into yarn, then fabric, then textiles. The textiles are then fabricated into clothes or other artifacts. There are three industrial processes available to spin yarn, and a...

 the yarn with a high number of twists per inch

Twist per inch

TPI is a term used in the textile industry. It measures how much twist a yarn has, and can be calculated by counting the number of twists in an inch of yarn.-Variation per yarn:...

. Fabrics with a large number of loose fibres have a higher tendency to pill. Also, knitted

Knitted fabric

Knitted fabrics is the third major class of fabric, after woven and nonwoven fabrics.-Elasticity, thickness and warmth:Compared to the other two classes, knitted fabrics are much more elastic, which accounts for their historical use in stockings and other clothing that requires changes in shape...

 fabrics tend to pill more than woven

Weaving

Weaving is a method of fabric production in which two distinct sets of yarns or threads are interlaced at right angles to form a fabric or cloth. The other methods are knitting, lace making and felting. The longitudinal threads are called the warp and the lateral threads are the weft or filling...

fabrics. This is because of the greater distance between yarn crossings in knitted fabrics than in woven ones. For the same reason, a tightly knitted object will pill less than a loosely knitted one. When a fabric is made of a blend of fibres where one fibre is significantly stronger than the other, pills tend to form as the weaker fibre wears and breaks, and the stronger fibre holds the pills onto the cloth.

Pills are generally undesirable. They are considered unsightly and are obvious marks of wear. They do not interfere with the functionality, unless a spot with a lot of pills turns into a hole in the fabric. This is because both pills and holes are caused by the fabric wearing—a pill is fibre that was in the cloth. After the pill forms the fabric is thinner there, increasing the likelihood that a hole will form.