What is Polyester resin?

Polyesters plastics are all around us in one form or another; it can be spun into fibres and micro fibres to make fabric for clothing, plastic bottles, photographic film, liquid crystal displays or LCD televisions, holograms and filters.

Polyester resins can be used to saturate any type of woven or chopped strand matting, such as fibre-glass, Kevlar and carbon fibre. Although any material that soaks up liquid like sponge, cotton, silk and paper, for example, all absorb the resin and become rigid, wet looking versions of themselves. Polyester GP resin and fibre-glass can be used to give hard  weather resistant shells to soft materials like urethane foam, which can be easily sculpted to form complex shapes.

Which Polyester resin should i use?

Polyesters come in a variety of colours including pink, blue, grey, beige, and white and transparent. They are all translucent to a certain extent which is an advantage

The polyester resins we use here in the workshop come in  three main: GP resin, Clear casting resin and Gel-coat. All of which can be used to encapsulate objects or support fillers, as long as the object or filler is relatively free of water content (or moisture) which could cause inhibition in Polyester resins.

It is also a good resin for casting, as there are a wide range of compatible pigments available and the transparency allows for changes in surface texture and appearance using a wide range of fillers and powders. This allows the user of polyester resins to transform this plastic. With imagination, we can learn to simulate many natural materials such as- water, sand, rock, precious metals and minerals, even the bark of a tree!

Important: When working with these resins you must wear protective gloves and, if you are using a it for a prolonged period or using a particularly large amount, the use of a respirator to protect yourself from the fumes* is advised. The fumes can make you feel light headed, and a little nauseous and can lead to long term health problems.

The future of Polyester’s

Polyester is the most commonly used resin in the marine, automotive and composite industry, recently however, new environmental protection laws are beginning to limit its use.

Polyester resin is available locally (Nottingham city) from-

Graham Robert Plastics’

Prices may vary:

£4.00 p/kg for GP resin

£8.00 p/kg for Clear casting resin

£6.00 P/kg for Gel-coat

The 3 main types of polyester resins are:

GP resin, Gel-coat and Clear casting resin


Pigmented GP resin casting’s


Gel-coat casting’s


Clear resin encapsulation


Clear resin casting

  1. *The fumes produced through curing process of Polyester resin is methanol. This must be expelled if curing is to take place. The rate of this molecular displacement varies with the amount of catalyst used and is known as condensation curing. This reaction takes place with all polymer resins and some Condensation silicones. So, the more catalyst you add the quicker the reaction time and the more concentrated the fumes become. The reaction also produces heat, known as an exo-thermic reaction. This heat combined with other toxic fumes create a nasty cocktail. So care should be taken when adding catalyst to Polyester resins.


Sand coated GP resin and Gel-coat casting


Cold-metal casting with GP resin