Sue Dale Tunnicliffe explains:
“Materials are all around. Some are made from naturally occurring substances from living organisms such as silk from silk worms, wool from sheep and other animals, cotton from the cotton plant and ropes from jute. Many everyday items are made from wood or stone, metals and non-metals. However, all things are made up of very small particles that join together, called molecules, and can be classified as solid, liquid or gas. Materials have differing properties depending on the small particles from which they are made. Some materials thrown away as rubbish are biodegradable and some are not biodegradable.” (p.127)
Ref: (emphases in blue bold, mine) Sue Dale Tunnicliffe (2013) Talking and Doing Science in the Early Years: A practical guide for ages 2-7. Routledge: Oxon and New York.