Sustainability Knowledge

GRP and Composites: Sustainability, Recycling and Suitability for External Seating & Planters

What is GRP?

GRP and composites aren’t a recently invented material.  In fact they were discovered around the start of the 20th century and have since been used heavily for industrial purposes.  GRP refers to Glass(fiber) Reinforced Plastic and it is a composite material that consists of a polymer matrix and glass fibers.  The polymer matrix, usually an epoxy/resin or similar, is the binder for the fibers in the structural laminate.  The glass fibers add strength to the composite.

Composites is the wider term for FRP and GRP.  As the name suggests, a composite is a material that is made from a polymer and different types of fibres.  FRP stands for fibre-reinforced polymer.  Although the fibres are usually glass fibre, as in GRP, other fiber types such as carbon or basalt are also utilised.  Therefore, FRP is a broader, more general term but it is often used interchangeably with GRP. 

How is GRP manufactured?

The manufacturing process is relatively simple.  The glass fibers, or strands, or woven together with the resin to create a flexible fabric.  GRP is a moulded product which means that it must be placed in a mould of the shape of the item it is required to take.  This is important, because it means it is very difficult to create bespoke shapes from GRP as each shape would require a new mould to be made first.  

Some GRP incorporates an aluminium oxide aggregate surface, which offers a higher resistance to long-term wear.

The emissions caused by the manufacturing of GRP are high – it is a processed product that goes through several production iterations.  However, compared to materials like steel, the production of the base resins and then the ‘weaving’ process has a smaller total environmental impact.

Properties of GRP

There’s a reason why GRP has become a mainstay for industrial purposes.  Here’s why:

Life expectancy of 20 years +.  Thanks to its composite strength, it has an excellent life expectancy.  However, for seating it is worth noting that even class 3 timbers such as Douglas Fir have a similar life expectancy.

Corrosion Resistance.  GRP is highly tolerant of even the most aggressive environments.  

Uniform Appearance.  If the GRP is coloured, the colour will be introduced before the fibres have been moulded.  This means that any wear and tear will be barely noticeable because the colour will be constant through the material.

There are other desirable properties, but they are mainly related to industrial concerns such as non-conductivity.

Can GRP be recycled?

GRP is inherently difficult to recycle.  The very nature of the interwoven fibres means it is almost impossible to break it back down again.

At present, the only facility for recycling GRP is in Germany which is not feasible for UK companies – transport emissions and transport cost.

Therefore, most GRP ends up going to landfill.  This is a big problem, because 50kt of end-of-life GRP is created each year.

Notice that, although difficult, it isn’t impossible to recycle GRP.  The way it can be done is by using it as fuel for cement kilns or grinding it to a fine powder to use as filler.  However, the problem with both these options is that it reduces the value of material to a point when it isn’t commercially viable to do so.  Second, a significant amount of energy is required to grind the GRP down.

Is GRP suitable for external seating & planters?

Although it does have its advantages, GRP is not ideal for external seating and planters.  

As mentioned above, one of the biggest problems is that GRP has to be moulded.  Therefore it is only available in set section sizes with very little scope for bespoke/custom work.

Also, there is the issue of fire risk.  GRP is a flammable material.  It will not melt like plastic, but it will burn.  This can be partially offset by treating it with a flame resistant treatment but this can only offer a certain level of protection.  

Finally, although boasting high impact resistance, GRP is susceptible to bending under load which isn’t a desirable characteristic for a bench.


In conclusion, GRP properties lend themselves much better to industrial purposes which, let’s not forget, is what it was invented for.  It is another question whether it should still be in use even for industrial purposes given that it can’t be recycled, but that will not be discussed here in any further detail.

Unfortunately its weak points are very relevant to external furniture and planters, especially the poor fire resistance.  For rooftop terraces and podiums in particular, this means that GRP options should not be considered, however cost effective or lightweight.


Logic Manufactured Bespoke, Telford Rd, Middlesbrough, TS3 8BL

© 2020 Logic Manufactured Bespoke | Privacy Policy | Terms & Conditions

Web Design by InnerCityDigital