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What Is GRP?

GRP stands for Glass Reinforced Plastic or Glass Reinforced Polymer. It is a very versatile material, which has a huge number of applications and uses. GRP is also often referred to as fibreglass (fiberglass in the US) or glass fibre composite. GRP also belongs to a larger family of products known as FRP, or Fibre Reinforced Plastics. We have compiled this in-depth guide to help you get to grips with what GRP is made of, how it is manufactured and what it can be used for.

What is GRP Material?

GRP is made up of a combination of glass fibre and polymer or plastic.

It has many desirable properties which include:

These properties make for a very versatile composite material with many different applications. Fibreglass can offer significant advantages over other materials like concrete, steel, other metals. It’s also a more adaptable material than non-reinforced thermoplastics such as nylon, polypropylene, or ABS (Acrylonitrile butadiene styrene).

So what is FRP?

FRP is short for Fibre Reinforced Plastic or Fibre Reinforced Polymer. Fibre reinforced plastic is a group included in what are collectively known as ‘composite’ products.  Composites are formed from a combination of a minimum of two different material types, chosen for their complementary physical and chemical properties.  You could think of them as ‘chemical cousins’ of alloys of metal.

In a fibre reinforced plastic, fibre strands are embedded in a polymer matrix resulting in both high compressive and tensile strengths in the finished products.  Glass fibre is used to produce GRP, but other fibres and resin combinations may also be used to create different materials.  These give the resulting composite materials different properties, making them suitable for a variety of applications.  Here’s an overview:

Fibres used in composites:

Resins used in composites:

Other chemicals are also added to composites to change the appearance and further enhance certain characteristics of the final product.


So, ‘FRP’ is an umbrella term used to describe an array of composite materials rather than any single type.  The finished materials have different properties and uses. This means that fibre reinforced plastics have a plethora of applications within the engineering and manufacturing industries.

What is GRP composite material made from and why do we use it?

GRP products are made from Glass fibre reinforced polymers, typically with a polyester or vinylester thermoset resin matrix. Thermoset polymers are formed by a chemical reaction, initiated by adding a catalyst, which causes an irreversible hardening of the resin.  This is coupled with reinforcement,  achieved by the incorporation of glass fibres during the production process. The fibres may be in the form of fine long strands, chopped stands or woven mats. The production techniques by which this is achieved are varied and can range from a simple manual process to one which is highly automated, utilising robotic machinery.  See below for further information on these processes.

Glass reinforced plastic properties

GRP has many useful properties which make the resulting GRP products very well suited to building and construction environments, be they internal or external.

Here are more key benefits of using glass reinforced plastic, to add to those listed above:

How are GRP products manufactured?

There are various production methods for GRP manufacturing, depending on the desired shapes, properties and intended uses for finished articles.

GRP moulding

Just for an example, an Evergrip GRP Industrial Moulded Mesh Walkway Grating Panel is produced by what is largely a manual process, using an open mould for curing.  These panels can measure anything up to around 4.0 x 1.5m and may also range between 12 – 60mm in thickness. Here, using a comb-like tool the glass fibre strands are woven back and forth across the length and width of the steel mould which has a cellular structure, to form the ‘skeleton’ of the finished of the panel.

The catalysed resin of the desired grade and colour is then poured into the heated mould until the product has cured and hardened.  The GRP gratings then have a coat of Aluminium Oxide grit adhered to the top surface.  The photos below show a typical example of the mould used.

GRP pultrusion

Structural profiled sections, including GRP Handrail profiles, are manufactured through an automated machine process known as Pultrusion.  The photos below show a machine-process schematic, factory layout (courtesy of Fiberline Composites a/s) and typical product sections that can be made using this technique.


GRP Hand Lay-up / Spray Lay-up Moulding

The Hand Lay-up process requires little in the way of tooling and is primarily used in low-volume production and bespoke made GRP products.  Manual skills present in the operatives will determine the quality of the achieved laminate.

The glass fibre reinforcement used is a woven or chopped strand mat and may also incorporate an inner coremat forming a sandwich between the layers of glass for added strength.  The materials are cut to size/shape before being laid into (or onto) the surface of a waxed (the release agent) open mould.  Resin is then applied with a roller or brush to fully saturate or ‘wet’ out the glass/core laminate. This is then left to fully cure in a suitably ventilated, warm drying area for several hours or overnight.  The part can then be removed, trimmed, top-coated/painted and polished as required.

Improved surface finishes may be achieved with an initial gelcoat layer applied to the mould before the reinforcement is placed into it. The top or presented surface of the finished part is the side which is in contact with the mould.  Here’s a short video outlining the process:

The Spray Lay-up technique is a semi-automated one, requiring a different manual skill set.  It utilises more expensive equipment and can often provide a computer-controlled resin/catalyst dosing system.  A pressurised spray gun incorporating a glass fibre ‘chopper’ head unit is utilised to apply the laminate to the mould in one continuous process.  The fibre is fed from a bobbin and rapidly chopped into rovings by the tool, directly into the stream of resin being applied to the mould.  Typical applications would include manufacturing baths, storage tanks & boat hulls. The process can be seen here:

GRP Resin Transfer Moulding

Resin transfer moulding is the process of injecting a mixed resin under pressure into a mould. This process of GRP moulding can produce smaller parts of consistently high quality and in production volumes. There is a longer video demonstration here which explains the process in full detail:

GRP Compression Moulding

This process consists of a preheated polymer being placed into an open mould cavity, before then being closed in by a top plug, in order for the material to contact all areas of the mould.  The process widely used in the production of parts for the automotive and transportation sectors and can incorporate epoxy resin systems. A long-established manufacturer in the United States explains the system here:

GRP Long Fibre Injection Moulding

An advanced, highly automated process for larger precision-made parts which require all the attributes of high strength and stiffness but with light weight.  Here the GRP moulding system uses a polyurethane matrix and long glass fibres applied by robot into a mould, where it is compressed, cures and hardens to the desired shape.

GRP Pultrusion

Pultrusion is also a highly mechanised industrial process used to create continuous lengths of GRP composite profiles.  These structural shapes are often associated with load-bearing applications, for example, channels or beam sections.  By means of this process, profiles have highly accurate and consistent cross-sectional dimensions and therefore predictable mechanical properties, allowing for the engineered design of structures.  Originally developed in the USA, this process has been in use for more than fifty years and the technology employed ensures high quality is reproduced in every production run.

Densely packed continuous glass fibre rovings are fed from multiple bobbins. Along with reinforcements, fibreglass mats and what is called a “surface veil”, they are then pulled by process machinery through a bath of resin. They are then passed through a high temperature and high-pressure mould, forming and curing the finished section shape.  The completed sections are then automatically cut to specified lengths.

The type and structural shape of these finished products are determined by the design of the mould.

Typical structural shapes include: Angles, Square Tube, I Beam, Channel, Round Rod, Round Tube

The finished GRP products are light in weight yet very strong, maintenance-free and are suitable for a huge range of applications replacing traditionally used metals and woods.  They have a smooth surface and are resistant to corrosion, providing a maintenance-free, long term and cost-effective solution.

We work closely with two established manufacturers of glass fibre pultruded products.  Through these relationships, Evergrip can offer a complete range of CE marked and certified fibreglass structural profiles with full European Technical Assessment (ETA) for use in construction in the United Kingdom and EEA market.  The products are manufactured by Fiberline Composites A/S of Denmark and represent the culmination of many years of research, development and investment.  Take a look at this brief video which shows pultrusion in action inside their ‘state of the art’ factory:

We hold stock in the UK of commonly used structural profiles in various sizes and thicknesses, the majority of which have enhanced fire-retardant properties to meet EN 13501 / BS 476 standards. We also welcome enquiries for new fibreglass profiles to be made, where there would be a significant volume usage.  We also offer design and engineering verification services along with fabrication and on-site installation of our GRP products.

Fibreglass Uses

GRP products have an almost limitless array of potential applications. With engineering verification and creative design, there are uses in most markets for products made partially, or entirely from GRP materials.  Here are some uses, arranged by sector:


- Fixed and portable work platforms

- Lamp posts

- Stair towers

- Bridges

- Roof trim and roof lights

- Gutters

- Glazing systems

- Cooling tower structures

- Green house structures

- Building panel sections

- Reinforcing rods (rebar)

- Sign posts

- Signs


Since 2001, Evergrip have been focused on applications for GRP composite materials in the fields of safe access and structural support.  With many long-serving staff, we have accrued valuable experience and knowledge in assisting clients in overcoming their problems in workplaces and public spaces, across almost all market sectors.

The wearing surfaces of all Evergrip GRP Anti-slip walkway and Grating products incorporate a coating of refined aluminium oxide aggregate, giving a near diamond-hard finish. This provides outstanding resistance to long term wear and most importantly, high levels of slip resistance, in both wet and dry conditions.

Buyer’s Tip: inferior quartz type grits available on some manufacturers’ products should be avoided, as these achieve only poor wear characteristics and hence, reduced product life and value.

We hope you have found the content of this article to be interesting and informative and we look forward to an opportunity of being of service to you.  Please feel free to browse our Products and Projects sections for more ideas and applications for glass reinforced plastic.

Evergrip Limited

Flaxley Road, Selby, North Yorkshire
YO8 4BG United Kingdom

PHONE: 01757 212744
Company Registered Number: 04186772
Registered for VAT Number: GB 773 5346 10

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27th March 2020

We are open for business

Covid 19 - Confirmation Statement

We would like to reassure all customers and enquirers that we remain open for business, while carefully following Government guidelines issued here:

The majority of our administration staff are working remotely and we have rostered production staff to make numbers available to meet demand.

We are able to provide the full range of our standard products from stock to serve any ongoing requirements you may have and will be pleased to receive any invitations to quote for future projects.

At the present time, in accordance with social distancing regulations we will not be conducting face to face meetings with business partners until further notice. However it may be possible to arrange video link meetings if required, please contact us for further information.

Collections of orders from our workshops are possible, by prior arrangement only please and visitors are reminded to observe the standard 2m distancing rules, for the safety of all.

Our transport partners are all providing us with a normal service.

We will update this statement if required and following any further guidance issued by the UK Government.

We wish you well.