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Properties of Composites


The Advantages and Properties of Composites

Composites are extremely versatile products - their benefits being:

High Strength to Weight Ratio

Fibre composites are extremely strong for their weight. By refining the laminate many characteristics can be enhanced. A common laminate of say 3 mm Chopped strand mat, is quite flexible compared to say a 3 mm ply. However it will bend a long way more than the ply before yeilding. Stiffness should not be confused with Strength. A carbon fibre laminate on the other hand, will have a stiffness of many times that of mild steel of the same thickness, increased ultimate strength, yet only be less than 1/4 of it's wgt.


 A standard Fibreglass laminate has a specific gravity in the region of 1.5, compared to Alloy of 2.7 or steel of 7.8. When you then start looking at Carbon laminates, strengths can be many times that of steel, but only a fraction of the wgt.

A DVD case lid was produced using carbon fibre to reduce the case's overall weight so that it could be carried as cabin baggage whilst travelling, and for improved security. It was used by support crew for the All Blacks during their 1999 Rugby World Cup campaign.

Fire Resistance

 The ability for composites to withstand fire has been steadily improving over the years. There is two types of systems to be considered:-

Fire Retardent - are self extinguishing laminates, usually made with chlorinated resins and additives such as Antimony trioxide. These release CO2 when burning so when the flame source is removed, the self extinguish. 

Fire Resistant - More difficult and made with the likes of Phenolic Resins. These are difficult to use, are cured with formaldehyde, and require a hi degree of post curing to achieve true fire resistance.

 Other materials are also becoming more readily available to be used as intumescent layers, which expand and blanket the surface, preventing spread of flame. There is a paint on coating usually applied to the back of the product laminate, plus a thin fibre film to go under the Gelcoat giving the outer surface a blanketing coat as well.

Fibreglass Developments Ltd produces a Fire Door as part of our SteridorTM range. Use of special Phenolic resin has allowed us to create the only fully tested Composite door in Australasia. Fire rated by BRANZ to 4 hours, this door is also approved by MAF as meeting all their Hygiene requirements.

Electrical Properties

Fibreglass Developments Ltd produced the Insulator Support straps for the Tranz Rail main trunk electrification. The straps, although only 4mm thick, meet the required loads of 22kN, as well as easily meeting  insulation requirements.

Chemical & Weathering Resistance

Composite products have good weathering properties and resist the attack of a wide range of chemicals. This depends almost entirely on the resin used in manufacture, but by careful selection resistance to all but the most extreme conditions can be achieved. Because of this, composites are used in the manufacture of chemical storage tanks, pipes, chimneys and ducts, boat hulls and vehicle bodies.

FDL manufactured architectural panels for the construction of the Auckland Marine Rescue Centre. Composite panels were chosen because of their ability to withstand salty sea side conditions without corrosion.


Almost any shade of any colour can be incorporated into the product during manufacture by pigmenting the gelcoat used. Costs are therefore reduced by no further finishing or painting. Soluble dyes can be used if a translucent product is desired.  

We do not however, recommend dark colours. These produce excessive heat on the surface which can lead to the surface deteriorating and showing print through, where the Resn matrix cures more and shrinks, bringing the fibres to the surface. In extreme cases delamination can occur.


Polyester resins are widely used to manufacture translucent mouldings and sheets. Light transmission of up to 85% can be achieved

Design Flexibility

Because of the versatility of composites, product design is only limited by your imagination.

Low Thermal Conductivity

Fibreglass Developments has been involved in the development and production of specialised meat containers which maintain prime cuts of chilled meat at the correct temperature for Export markets. They are manufactured using the RTM process, with special reinforcing and foam inserts.

Manufacturing Economy

Fibreglass Developments produces several models of fuel pump covers for Fuelquip. Fibreglass is an ideal material for producing items of this type for many reasons, including being very economical.

Because of its versatile properties, fibreglass can be used in many varied applications.