The man-made plastic (or polymer) of which Terylene sails and ropes are made (Dacron in the USA), and which is used in the building of ‘glassfibre’ hulls. When used in fibre form it is a ‘saturated’ resin. In fluid form, as it comes to the boatbuilder for hull moulding, it is known as ‘unsaturated’, and is commonly in the form of a solution of polyester in styrene. When a catalyst is added the styrene cross-links the molecular chains of the polyester to form a polymer, which is a network of linked molecules. This crosslinking is known as curing, and it is a non-reversible process.