To compare materials using data, look at the same property for each material, such as density, melting point or strength, and say which is higher or lower. Typical values help: steel has a density of about 7.8 g/cm3 and melts at about 1500 °C, whereas poly(ethene) has a density of about 0.9 g/cm3 and softens at about 120 °C.
Glass and clay ceramics are hard, stiff and have high melting points. They are poor conductors of heat and electricity, and they are strong when squashed, but they are brittle, so they shatter when hit. Glass is also transparent. Polymers have low density, low melting points, so they soften when heated, and they are poor conductors, and many are flexible. Metals are strong, have high melting points, are good conductors of heat and electricity, and are malleable, so they can be hammered into shape. They are usually denser than polymers.
A composite is made of a reinforcement, such as fibres, embedded in a matrix that binds it together. Fibreglass has glass fibres in a plastic matrix, and concrete has an aggregate of gravel and sand in cement. Composites combine the useful properties of both parts, for example being strong yet light.