Composites are a mixture of more than 1 material so that we can take advantage of the best properties of each material.
Safety glass is glass (ceramic) around a wire mesh (metal). The glass is hard and transparent. The metal is tough (it can take impacts) and flexible (it can bend without breaking). The composite is hard, transparent, tough, and much more difficult to break.
Fibreglass:The hard plastic used is tough and hard but cracks easily. The glass fibres buried within it makes it hard to crack. They stop the cracks getting bigger.