GRP Materials: Composition, Properties and Manufacturing

GRP, or Glass Reinforced Plastic, is a composite material made from glass fibre reinforcement combined with a resin matrix. The result is a material that combines the strength of glass with the versatility of plastic, offering a genuine alternative to steel, aluminium and timber in industrial and commercial applications. Engineered Composites has manufactured GRP materials from our Chester and Saltney facility for over 40 years, supplying products to ISO 9001:2015 standards for the rail, construction, water utility, marine and defence sectors.

What GRP Materials Are Made From

Every GRP material begins with two components. Glass fibre provides the strength and stiffness, carrying the structural load, while a resin matrix, typically polyester, vinyl ester or epoxy, binds the fibres together and protects them from moisture, chemicals and UV exposure. Neither component performs on its own, it is the combination that gives GRP its distinctive balance of strength and weight.

How GRP Materials Are Manufactured

Most structural GRP materials supplied by Engineered Composites are produced by pultrusion. Continuous strands of glass fibre are drawn through a resin bath, saturating the fibres before they pass through a heated die that cures the resin and sets the finished profile shape. The process runs continuously, producing long, consistent lengths of profile to a fixed cross-section, which is what allows GRP materials to be manufactured to the tight dimensional tolerances required by BS EN 13706.
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How GRP Materials Are Manufactured

Most structural GRP materials supplied by Engineered Composites are produced by pultrusion. Continuous strands of glass fibre are drawn through a resin bath, saturating the fibres before they pass through a heated die that cures the resin and sets the finished profile shape. The process runs continuously, producing long, consistent lengths of profile to a fixed cross-section, which is what allows GRP materials to be manufactured to the tight dimensional tolerances required by BS EN 13706.

Properties of GRP Materials

GRP materials are prized for a specific combination of properties rather than any single characteristic. They are highly resistant to corrosion from chemicals, water and weathering, which makes them well suited to marine, coastal and wastewater environments where steel would need ongoing protection. They are electrically non-conductive, an important safety property for rail, defence and data centre applications. GRP materials also offer a strong strength-to-weight ratio, weighing significantly less than steel for comparable structural performance, and require minimal maintenance over a design life of 50 years or more.

GRP Materials Compared to Steel, Aluminium and Timber

Unlike steel, GRP materials do not rust or require repainting, which removes a recurring maintenance cost over the life of an installation. Compared to aluminium, GRP offers better chemical resistance and does not suffer from galvanic corrosion when in contact with dissimilar metals. Against timber, GRP materials do not rot, warp or require chemical treatment, and their performance is far more consistent from batch to batch. These characteristics are why specifiers increasingly choose GRP materials for structural framing, grating, handrails and fencing in place of traditional materials.

GRP Materials from Engineered Composites

All GRP materials manufactured by Engineered Composites meet BS EN 13706 for pultruded profiles and BS EN 4592 for grating and flooring products. We hold RISQS accreditation for rail sector supply and JOSCAR registration for defence projects, and our quality management is certified to ISO 9001:2015. Materials are held in stock for next-day UK delivery, with in-house capability to manufacture bespoke items to project specification.
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To find out more about our GRP material range, or to discuss a specific product requirement, get in touch with our technical team, or browse our full range of GRP products.