Synthetic resins are divided into two classes: 

• thermoplastic resins – they remain plastic after heat treatment,

• thermosetting resins – they become hard  and not flexible after heating.

Synthetic resins are not clearly differentiated from plastics.   

Fibreglass is a synthetic resin, usually polyester, which has been reinforced with laminations of glass fibre. It is an extremely strong, hard, lightweight and durable material. As a material for sculpture, it is often coloured by means of fillers and pigments. It is possible to model fibreglass, but more usually it is cast as a laminated shell. 

Fibreglass can be recycled, however, the process is not simple as it is a composite material which needs special treatment to separate glass fibre and resin and make them suitable for reusing.