Materials that bend and stretch


In this picture you can see that a wire is bent into a new shape and then bent back to its original shape. The wire can do this because it is flexible. When a flexible material is bent, part of it stretches at the point where it is bent, while the opposite side shrinks. This helps to hold the material in its new shape. It does not make the material spring back. A flexible material can be bent many times and in many ways before it breaks.

Where do the fibres in clothes come from?
Some fibres are natural materials and others are manufactured materials. Cotton, wool, silk and flax are natural fibres. Nylon is just one of many manufactured fibres. Some manufactured fibres have strange names such as polyester or acrylic. You could look at the labels in your clothes to find what fibres have been used to make them. You may find some clothes are made from natural fibres and manufactured fibres that have been mixed together.

How are the tiny fibres made into yarn?
They are twisted together to make thicker threads called yarn. This process is called spinning. The yarn is much stronger than the individual fibres. The ends of some of the fibres stick out of the yarn. This is what makes the fuzzy layer on the surface of woollen cloth, for example.


How are the yarns held together in cloth?
Most yarns, like cotton, are woven together, but some, like wool, can also be knitted. Woven cloth is used for making shirts, blouses, skirts, trousers and jackets. Knitted cloth is used for making pullovers and certain kinds of hats. In the weaving process one yarn is made to go over and under another yarn. When something is knitted, one yarn is made into loops which interlock with each other.



Is weaving used to make anything else besides clothes and fabric?
Yes. It is used to make baskets. If you look at a basket you will see how the strands of material have been made to go over and under each other. Baskets may be made from long strips of bamboo, cane from a palm tree or raffia from palm leaves. Long sticks may be woven together to make a fence. In the past, houses were made that had walls made of woven flexible hazel twigs that were coated in a mixture of clay and horsehair (composite material).
How are ropes made?
Ropes are useful because they are both strong (when pulled) and flexible. Some ropes are made by twisting strings together. Others are made by a process called plaiting. Some people have their hair put into plaits, and ropes are plaited in the same way.
To plait a rope you take three strings and tie them at one end. This end is then placed on a hook (or toe, in the case of the man in the picture below). One string is placed over another and the third is placed over that. The string at the bottom is then placed over the top and the one in the middle placed above that. By repeating these movements and moving further down the strings, a rope is plaited together.



Do all flexible materials have fibres?
No. Metal is not made from fibres. It is made from tiny crystals that grip together. When a metal is bent, the crystals slide past one another.
Metals sheets are flexible. Look at aluminium cooking foil to check this is true. Metals can be drawn into long thin flexible wires. Copper is a particularly flexible metal and is used in electric cables.
Many plastics are also flexible. Plastic bags are made of sheets of flexible plastic, for example.


Does making a material into a fibre help make it flexible?
Yes it does. A rope made of metal strands is far more flexible than a solid rod of the same size. Glass sheets are not flexible and glass snaps easily. However, when glass is made into long fibres, they can be made into flexible cables and used for sending light beams. These are called optical fibres and they are used for modern communications. In 1988 a cable made from glass fibres was laid across the Atlantic Ocean to carry messages between North America and Europe.