Insights: Polymers edge into metal’s domain as defence materials shift gathers pace

High-performance plastics and composites drive a structural shift towards lighter, more efficient and resilient systems.

Against this background, it is not surprising that traditional metals such as steel and aluminium are increasingly being replaced by advanced polymers and fibre composites. This is no longer about marginal improvements, but a clear technological shift.

At the centre are high-performance thermoplastics such as polyether ether ketone (PEEK), polyetherimide (PEI), polytetrafluoroethylene (PTFE) and polyamide 6 (PA6).

 These materials have, in a short period, established themselves in critical applications, ranging from structural components and enclosures to fasteners, bearings and seals in vehicles, weapons systems and sensor technologies.

PEEK in particular has assumed a prominent role as a metal substitute. With a density of approximately 1.3 g/cm³, the material is significantly lighter than both aluminium and steel, while—especially in carbon fibre-reinforced form- it can offer extremely high strength. 

The combination of low weight, temperature resistance and chemical resistance allows PEEK in many cases to replace metal without compromising performance. Unlike metals, it also requires no corrosion protection, which simplifies both design and maintenance.

One of the most critical applications for polymers in defence is ballistic protection. Here, materials such as ultra-high-molecular-weight polyethylene (UHMWPE) and aramid fibre, known under brand names such as Kevlar, have become indispensable. 

UHMWPE combines extreme impact resistance with low weight and is used in everything from protective plates and helmets to lighter armour solutions for vehicles. 

Aramid composites play a central role in body armour, where their ability to absorb and disperse energy can be directly life-saving. For transparent protective applications, such as visors and protective glazing, polycarbonate is the standard material due to its high impact resistance and optical clarity.

At the same time, the development of unmanned systems, particularly drones, is driving a rapid increase in the use of fibre-reinforced plastics. Carbon fibre-reinforced polymers (CFRP) offer very high stiffness relative to their weight and are therefore used in load-bearing structures, aircraft components and enclosures for advanced electronics. 

Glass fibre-reinforced polymers (GRP) serve another important function where electromagnetic properties are critical, for example in antenna structures and radomes, where the material must not interfere with signals.

In electronics and optronics, polymers serve a dual function as both protection and an integrated part of the system. Materials such as PEI and specially modified polycarbonates are used where requirements for flame retardancy and temperature resistance are high. 

At the same time, polymers such as PEEK provide good electrical insulation and controllable thermal conductivity, which is critical in densely packed systems. Their resistance to moisture, de-icing agents and chemicals makes them particularly suitable for operation in demanding environments.

An important explanation for the rapid uptake of polymers lies not only in their properties, but also in their manufacturing advantages. Processes such as injection moulding, extrusion and additive manufacturing make it possible to produce complex components with a high degree of functional integration. 

This means that multiple parts can be replaced by a single component, reducing weight, assembly costs and potential sources of failure. The elimination of corrosion protection, and the risk of issues such as cold welding in moving joints, are additional advantages.

Colouration in the defence industry is also governed by function rather than aesthetics. Polymers are pigmented in subdued shades such as black, green, brown and grey to achieve effective camouflage, while white is used in Arctic environments. Material selection and surface finish are thus an integral part of the systems’ tactical function.

The outlook is therefore clear. 

By 2030, high-performance polymers are expected to continue replacing metals in an increasing number of applications, driven by the need for lower weight, longer range and higher system efficiency. Carbon fibre composites are expected to be the primary growth driver, while PEEK is set to strengthen its position in advanced applications where extreme requirements converge. At the same time, PEI is expected to expand in more standardised, flame-retardant-critical components.

Overall, polymers are no longer a marginal alternative, but a central part of the modern defence industry’s materials strategy. In a sector where every gram counts and every material choice can affect operational capability, plastics - paradoxically- emerge as some of the highest-performing materials on the battlefield.