Semi-conductors

There is also a small group of materials called semi-conductors. These have both conducting and insulating properties and they are used to make electronic components. The way in which a semi-conducting material is connected to a power supply determines whether it will conduct an electrical current or prevent it from flowing.

Types of materials

Materials are grouped into five main categories, based on what they are made from:

· wood

· metals

· polymers

· ceramics

· composites

Smart materials

In addition, some new materials have been developed with properties that can react to changes in their environment. Although each of these new materials fall into one of the five types, they are often classed as a separate group called smart materials.

Wood

There are two types of wood: softwood and hardwood. These names do not refer to the properties of the wood: some softwoods can be hard and some hardwoods can be soft.

Softwoods, such as pine, come from coniferous trees. These keep their leaves all year round. They can be grown in renewable managed forests. This means that more wood can be grown to replace that being used.

Deciduous tree

Coniferous tree

Hardwoods, such as oak or beech, come from deciduous trees. These lose their leaves each winter. They tend to grow slower than softwoods.

Wood is time consuming to process and only comes in relatively narrow widths, due to the sizes of tree trunks. The properties of a piece of wood may vary in different directions, depending upon the direction of the grain.