How thermally conductive plastics could be a more sustainable and performance-optimised aluminium alternative

Thermal management remains one of the defining engineering challenges across sectors ranging from LED lighting and power electronics to electric vehicles and industrial motors

As power densities rise and packaging volumes shrink, engineers are under pressure to dissipate heat efficiently while also addressing cost, manufacturability and environmental performance. Against this backdrop, thermally conductive plastics are increasingly being evaluated as alternatives to traditional die-cast aluminium solutions.

According to Dr Ben Hargreaves, sales area manager – UK & Ireland at Lati UK, advances in polymer compounding, certification and lifecycle assessment are enabling these materials to move beyond niche applications and into mainstream engineering use. “We spend a huge amount of time, effort and investment ensuring our materials meet demanding regulatory standards,” he explained during a presentation at the recent Advanced Engineering exhibition in Birmingham, UK. “Across our portfolio we have around 50 grades with active UL Yellow Cards, alongside rail certification and other sector-specific approvals.”

MATERIAL PLATFORMS AND FILLERS

At a fundamental level, thermally conductive plastics are created by combining a polymer matrix with thermally conductive fillers. While the underlying concept is straightforward, the execution is highly specialised. “In very simple terms, we take a polymer, add a thermally conductive filler, and that gives us our compound,” says Hargreaves. “In practice, there is a great deal of know-how required to balance thermal, mechanical and processing performance.”

The fillers typically fall into two categories: graphite-based and ceramic-based. Graphite fillers enable the highest thermal conductivities achievable in polymers, reaching values of up to around 30W/m·K. However, graphite also introduces electrical conductivity, which can be unacceptable in certain applications. Ceramic fillers, by contrast, offer electrical insulation but lower thermal conductivity, typically in the high single digits up to around 10W/m·K.

“Graphite-filled compounds give you the best thermal performance, but you have to accept some electrical conductivity,” Hargreaves noted. “Ceramic-filled systems won’t get you to the same conductivity levels, but they are electrically insulating, colourable, and non-marking, which can be critical in many electrical and electronic applications.”

Both material families can retain good mechanical properties, dimensional stability and processability, including mouldability, machining and welding. Flame-retardant variants are also available, particularly for ceramic-filled systems.

ANISOTROPHY AND DESIGN IMPLICATIONS

One of the key differences between thermally conductive plastics and metals lies in anisotropy. Aluminium is isotropic, meaning its thermal conductivity is the same in all directions. Filled polymers, particularly those using high aspect ratio fillers such as graphite or hexagonal boron nitride, exhibit direction-dependent conductivity due to filler alignment during injection moulding.

“You tend to get much higher in-plane thermal conductivity than through-plane,” explained Hargreaves. “That’s not necessarily a problem, but it means you cannot take a ‘black metal’ approach and simply copy an aluminium design in plastic.”

Instead, engineers must consider part geometry, gate locations, flow paths and rib or fin design to ensure heat is conducted away from sensitive components and dissipated effectively at the surface. Lati uses mould flow analysis combined with thermal simulation to predict filler orientation and heat dissipation performance before tooling is cut. “This allows us to give customers a very accurate picture of how the final part will behave thermally,” added Hargreaves.

RETHINKING HEAT DISSIPATION METRICS

A common objection to thermally conductive plastics is their lower conductivity compared with aluminium, which typically offers around 100W/m·K. However, Hargreaves argued that thermal conductivity alone is not the dominant factor in many real-world applications.

“For the majority of natural convection applications, conductivity is not what determines how quickly heat is dissipated,” he says. “Once heat reaches the surface, convection is the critical mechanism.”

Extensive testing, particularly in the lighting sector, has shown that plastics with thermal conductivity around 10W/m·K can perform comparably to aluminium heat sinks under natural convection conditions. Surface emissivity can also play a role, with matte, dark polymer surfaces sometimes offering better radiative heat transfer than shiny metal finishes.

There are, of course, limits. Forced convection, very high heat fluxes or applications competing with low-cost extruded aluminium profiles remain areas where metals retain a clear advantage.

SUSTAINABILITY AND LIFECYCLE PERFORMANCE

Environmental performance is becoming an equally important selection criterion. “Sustainability is very, very important to us as a company,” said Hargreaves. “That’s why we’re increasingly offering materials with bio-based or recycled content that deliver exactly the same mechanical, thermal and fire performance as virgin grades.”

On a raw material basis, primary aluminium carries a global warming potential (GWP) of roughly 10kg CO2 per kilogram, while thermally conductive plastics can be significantly lower. Even when recycled aluminium is considered, a like-for-like comparison by mass is misleading due to density differences.

“A more realistic comparison is GWP per part, not per kilo,” Hargreaves explains. “When you do that, thermally conductive plastics can show a clear advantage.”

The benefits are amplified further by the use of chemically recycled polymers. Lati has demonstrated that switching from virgin nylon 6 to chemically recycled nylon 6 with identical filler content can roughly halve the GWP of the compound, even before accounting for processing, transport or end-of-life considerations.

ASSESSING THE APPLICATIONS

Typical applications include LED luminaires, electrical enclosures, power distribution components, motors and automotive electronics, particularly in electric vehicles where electrical insulation and weight reduction are critical. As devices become more compact and power densities increase, demand for materials that combine thermal performance, design freedom and sustainability is set to grow.

“Thermally conductive plastics are not a universal replacement for aluminium,” Hargreaves concluded. “But in the right applications, with the right design approach, they can be cost-competitive, environmentally advantageous and technically robust.”