Important fibres and their properties

Cotton grows as fibres attached to the seeds inside cotton pods (bolls). The fibres are separated from the seeds by ginning. Cotton is a cellulosic staple fibre, about 1 to 5 cm long.

• It looks dull, feels slightly rough, and is fairly heavy.
• It is highly absorbent and conducts heat away from the body, so it is cool and comfortable in summer.
• It wrinkles easily, but is strong, especially when wet, and easy to wash.

Linen comes from the stems of the flax plant. The fibres are freed by retting, letting the stems rot in water so the fibres separate. Linen fibres are longer, finer, stronger and more lustrous than cotton, and also absorbent and cool, but they do not take dye as brightly. Jute and hemp are coarse bast (stem) fibres used for ropes, sacks and gunny bags.

Wool is sheared from sheep (and from goats, rabbits and camels). The raw wool is scoured (washed) to remove grease and dirt, and carbonised (treated with acid) to remove plant matter. Wool is a protein fibre, 4 to 40 cm long.

• Its natural crimp (waviness) gives elasticity and traps air, making it warm.
• It has low strength but excellent resilience: woollens resist wrinkling.
• It can absorb a lot of moisture without feeling wet.

Silk is a protein filament spun by the silkworm as it makes its cocoon. Raising silkworms is called sericulture. The filament is unwound (reeled) from the cocoon.

• It is long, fine, smooth and highly lustrous, strong for its fineness, with good elastic recovery.
• Wild silk, such as tussar, comes from silkworms living in forests; it is coarser, less even and brownish.

Manufactured fibres:

• Rayon: regenerated cellulose from wood pulp. It looks silk-like, is absorbent like cotton, but is weaker, especially when wet.
• Nylon: the first true synthetic, made into stockings from 1940. Very strong, resistant to abrasion, elastic; used in ropes, stockings and sportswear.
• Polyester (sold as Terylene, Terene): strong, wrinkle-resistant, absorbs very little moisture, so it dries quickly but can feel hot. It is often blended with cotton or wool.
• Acrylic (sold as Cashmilon): soft and wool-like, and cheaper than wool, so used for sweaters and blankets.
• Spandex (Lycra): very elastic; small amounts are blended into fabrics for stretch.

The burning test helps identify fibres. Do it only with a teacher, holding a tiny piece in tweezers over a small flame:

• Cellulosic fibres (cotton, linen, rayon) burn quickly with a yellow flame, smell like burning paper and leave a soft grey ash.
• Protein fibres (wool, silk) curl away from the flame, burn slowly, often go out by themselves, smell like burning hair and leave a crushable black bead.
• Synthetics (nylon, polyester) melt and shrink from the flame, and leave a hard bead that cannot be crushed.