Materials such as polystyrene, nylon, polypropylene and polythene can be used in a process called injection moulding. These are thermoplastics - this means when they are heated and then pressured in a mould they can be formed into different shapes.
The DVD Storage unit seen opposite has been made in one piece using this process.
An animation of an injection moulding machine is shown below. The product being produced is the DVD / CD storage unit seen opposite.