Guide to composites
What are composites?
Composite materials combine high‑performance fibres with a polymer matrix to form lightweight, corrosion‑resistant structures whose properties can be precisely engineered for specific loads and environments. By working together, fibres and resins deliver performance characteristics that neither material can provide alone, which explains why fibre‑reinforced plastics (FRP) are widely used across modern industries.
Here At Exel, composites are designed and manufactured using continuous processes such as pultrusion and pull‑winding, enabling consistent quality, predictable performance and scalable solutions for demanding applications.
Composite material structure showing reinforcing fibres combined with a polymer matrix to form a composite.
In simple terms:
- Fibres provide strength and stiffness.
- The polymer matrix (resin) holds the fibres together, transfers loads between them and protects them from environmental exposure.
By controlling how fibres and resin work together, composite properties can be aligned with specific load cases and operating conditions. Unlike monolithic materials such as metals, composites do not rely on uniform behaviour in all directions — performance follows the fibres.
What reinforcing fibres do in a composite
Reinforcing fibres carry most of the load in a composite material. Their primary role is to provide strength and stiffness, while the surrounding resin supports and protects them. In practice, the mechanical performance of a composite is largely defined by the fibres that are used and how they are arranged.
Key aspects controlled by the fibres include:
Strength and stiffness
Fibres take tensile and compressive loads. Higher fibre content increases load‑carrying capacity and stiffness, particularly in the fibre direction.
Weight efficiency
Fibres deliver high mechanical performance at low weight, giving composites excellent strength‑to‑weight and stiffness‑to‑weight ratios compared to metals.
Directional performance
Fibre orientation determines where the composite is strong and stiff. Aligning fibres with load paths allows material to be placed only where it contributes to performance.
Different fibre types are selected depending on performance requirements, cost targets and operating conditions. Common reinforcements include glass fibres for cost‑effective strength and durability, and carbon fibres where high stiffness and low weight are required.
For a more detailed look at common reinforcement types, fibre architectures and how they are used in practice, see Reinforcements in composites.
What the resin matrix does in a composite
The polymer matrix plays a critical supporting role in a composite material. While fibres provide strength and stiffness, the resin enables those fibres to work together as a structural system.
In practice, the resin is responsible for several key functions:
- Load transfer
- The resin distributes loads between individual fibres, allowing them to act together rather than as separate elements. This load sharing is essential for predictable and repeatable mechanical performance.
- Environmental protection
- The resin shields fibres from moisture, chemicals, UV exposure and other environmental factors that could degrade performance over time.
- Surface quality and durability
- The matrix defines the surface finish of the composite and contributes to properties such as chemical resistance, wear resistance and fire behaviour.
Different resin systems are selected depending on operating environment, temperature, regulatory requirements and performance targets. Common thermoset matrices include polyester, vinyl ester and epoxy, each offering a different balance of durability, processing characteristics and resistance to heat or chemicals.
Together with the fibres, the resin system determines the composite’s long‑term behaviour. A deeper overview of typical resin systems, their properties and selection criteria is available in Resin choices for composites.
Why composite materials are tailorable
Unlike metals or plastics, composites are engineered rather than selected. Their properties are not fixed by a single material choice but are defined by how different elements are combined and arranged. This makes it possible to design composite structures that perform exactly where required — without unnecessary weight or material.
Tailorability in composites comes from several interdependent design variables:
- Fibre type
- Glass, carbon and other fibres offer different balances of strength, stiffness, weight and cost. Selecting the appropriate reinforcement allows performance to be matched to structural and economic requirements.
- Fibre orientation and architecture
- Because fibres carry load primarily along their length, aligning them with expected load paths is critical. Directional fibre placement enables stiffness and strength to be concentrated where they are needed most, rather than uniformly in all directions.
- Resin system
- The matrix influences environmental resistance, temperature performance, surface quality and long‑term durability. Resin selection ensures that the composite performs reliably under its intended operating conditions.
- Profile geometry and wall thickness
- Composite cross‑sections can be designed to achieve stiffness through shape as well as material. Deeper profiles, closed sections and local reinforcement can be used to optimise performance without a proportional increase in weight.
By adjusting these variables together, composite structures can be engineered for specific load cases, environments and lifetime requirements. This level of control is not achievable with isotropic materials such as steel or aluminium, where properties are the same in all directions and excess material is often required to meet peak loads.
At Exel Composites, this tailorability is enabled through continuous manufacturing processes such as pultrusion and pull‑winding. These processes allow fibre orientation, resin systems and geometry to be precisely controlled and repeated at industrial scale — translating design intent into consistent, predictable performance across demanding applications
How composites differ from metals and plastics
Composite materials sit between metals and plastics — and in many structural applications, they outperform both. The difference lies not in a single property, but in how performance, durability and design freedom are combined through material design.
Unlike metals and most plastics, which have fixed and uniform properties, composites are engineered systems. By controlling fibre type, fibre orientation, resin system and geometry, their behaviour can be aligned closely with specific loads, environments and lifetime requirements.
Key differences
Property / Aspect |
Composites (FRP) |
Metals (e.g. steel, aluminium) |
Plastics (unreinforced) |
Strength‑to‑weight ratio |
High: strength and stiffness achieved with low mass through fibre reinforcement | Moderate to high: increased strength usually means increased weight | Low – limited load‑bearing capability |
Stiffness |
Directional and tailorable through fibre type and orientation | High but fixed and isotropic | Low to moderate |
Density / weight |
Low | High (steel) to medium (aluminium) | Low |
Corrosion resistance |
Excellent – non‑metallic, no rust or galvanic corrosion | Requires coatings or protection in corrosive environments | Generally good |
Electrical conductivity |
Non‑conductive by nature (can be made antistatic on request) | Conductive | Non‑conductive |
Thermal conductivity |
Low | High | Low |
Thermal expansion |
low and engineerable: similar to steel in fibre direction | Fixed: Low for steel, medium for aluminium | High and less controllable |
Directional behaviour |
Anisotropic – properties follow fibre direction | Isotropic – same properties in all directions | Mostly isotropic |
Design flexibility |
High – material, orientation and geometry co‑designed | Limited to shaping and alloy choice | Limited by low structural performance |
Durability & fatigue |
High when properly designed | Good, but fatigue and corrosion must be managed | Limited for structural use |
Maintenance over lifetime |
Low in demanding environments | Often high due to corrosion and wear | Low, but limited structural use |
Engineering approach |
Engineered material system | Selected material | Selected material |
This overview highlights why composites are often chosen when lightweight performance, corrosion resistance and long‑term durability are critical.
Bringing it together
The fundamental distinction is that metals and plastics are selected, while composites are engineered. Rather than adapting a design to a fixed material, composites allow material behaviour to be aligned with the application itself — reducing unnecessary weight, improving durability and enabling efficient structural solutions.
This is why composites are increasingly used in transport, infrastructure, electrical and industrial applications where predictable performance over long service lives is required.
Where composite materials are used
Composite materials are chosen where lightweight performance, durability and low lifetime maintenance are critical. Their ability to combine structural efficiency with corrosion resistance and electrical insulation makes them suitable for demanding environments across multiple industries.
Rather than being defined by a single sector, composites are applied wherever traditional materials struggle to meet long‑term performance, weight or environmental requirements.
Transport
In transport applications, composites help reduce weight while maintaining structural integrity and durability — directly supporting efficiency and long service life.
Reducing weight contributes to improved energy efficiency, while corrosion resistance lowers maintenance needs over the lifetime of vehicles and infrastructure.
Buildings and infrastructure
In buildings and infrastructure, composites are used where strength, durability and environmental resistance are required over decades of service.
Common applications include:
- Structural profiles and beams
- Frames, walkways and access structures
- Façade elements and glazing support systems
Composites are particularly well suited to outdoor and corrosive environments where steel would require extensive protection or ongoing maintenance.
Electrical and energy applications
Because fibre‑reinforced composites are electrically non‑conductive and corrosion resistant, they are widely used in electrical and energy infrastructure.
The combination of mechanical performance and inherent insulation properties makes composites a reliable choice in safety‑critical installations.
Tubes and profiles
Continuous composite manufacturing enables a wide range of constant cross‑section profiles and tubes to be produced with consistent quality and performance.
Applications include:
- Structural tubes and beams
- Custom cross‑sections designed for specific load cases
- Profiles used in industrial, electrical and infrastructure systems
By tailoring fibre orientation, wall thickness and geometry, composite tubes and profiles can be optimised for stiffness, strength and durability without unnecessary weight.
From applications to solutions
These examples show where composite materials are used in practice — but performance always depends on how the material is engineered and manufactured.
To explore Exel’s full sector portfolio and manufacturing expertise, visit Composite solutions.
Composite manufacturing methods at Exel Composites
The performance of a composite structure depends not only on material design, but on how consistently that design can be manufactured. At Exel Composites, this is achieved through continuous manufacturing processes that enable precise control of fibre placement, resin content and geometry at industrial scale.
These processes are particularly well suited to producing high‑quality composite profiles, tubes and panels with repeatable properties and predictable performance over long service lives.
Pultrusion
Pultrusion is a continuous manufacturing process in which the reinforcing fibres, along with fabrics or mats where required, are pulled through a resin bath and then through a heated die to form a constant cross‑section profile.
At Exel, pultrusion enables:
- High fibre volume fractions and consistent mechanical performance
- Excellent dimensional accuracy and surface quality
- Efficient production of beams, profiles and flat sections for structural use
Because fibres are aligned along the length of the profile, pultruded composites are especially efficient in applications where loads are carried predominantly in one direction.
Pull‑winding
Pull‑winding combines pultrusion with controlled fibre winding around the profile during manufacture. This allows fibres to be placed not only in the longitudinal direction, but also circumferentially or at defined angles.
This process enables:
- Improved transverse and torsional performance
- Enhanced strength in tubes and round or hollow profiles
- Greater control over load‑bearing behaviour in multiple directions
Pull‑winding is particularly valuable in applications where bending, torsion or internal pressure play a significant role.
Why continuous processes matter
Continuous manufacturing allows composite structures to be produced with repeatable quality, controlled fibre architecture and predictable performance — attributes that are critical in structural, electrical and infrastructure applications.
At Exel Composites, these processes translate engineered material concepts into reliable, scalable solutions that meet demanding technical and lifetime requirements across industries.
Designing and working with composites
Composite materials are not only structural — they are also practical to design with and work with. Many fabrication and assembly methods are familiar to engineers and installers used to working with metals or plastics.
Composite profiles can be:
- Cut, drilled and machined using standard workshop tools
- Joined using mechanical fasteners, adhesives, or a combination of both
- Integrated with metals or other materials, provided thermal expansion and environmental factors are considered during design
The key difference lies in the design approach. Composites reward early collaboration and holistic thinking. Because material behaviour is engineered rather than fixed, decisions made early in the design process have a significant impact on performance, weight and overall system complexity.
At Exel Composites, engineers work closely with customers to optimise geometry, fibre architecture and resin selection. This often allows assemblies to be simplified, components to be integrated, and total system weight to be reduced — benefits that cannot be achieved by material substitution alone.
Frequently asked questions about composites
Are composites stronger than steel?
Per unit weight, yes. While absolute stiffness differs, composites can be designed to achieve equivalent or higher structural performance at significantly lower mass.
Do composites corrode or rust?
No. Fibre‑reinforced composites are inherently corrosion resistant and well suited to harsh or chemically aggressive environments.
Can composites be repaired?
Yes. Standard repair techniques exist, similar to those used for wood or marine composite structures. Repair methods depend on the application and service requirements.
Are composites fire safe?
Fire behaviour depends on the resin system used. Exel manufactures fire‑retardant composite materials that meet relevant European and industry‑specific standards.
Are composites difficult to machine or install?
No. With appropriate tools and guidance, composite profiles are straightforward to machine, assemble and install.
Why work with Exel Composites?
Exel Composites is one of the world’s largest pultrusion and pull‑winding specialists, with decades of experience in designing and manufacturing continuous composite solutions.
Customers bring their application knowledge. Exel brings deep composite expertise — from concept development and material selection to industrial‑scale, repeatable production. This partnership approach helps ensure that composite solutions deliver predictable performance, long service life and commercial viability.
