Sentherm conductive polymers match aluminum thermal performance, cut weight

Replacing aluminum with polymers for thermal conduction applications sounds like trading a sports car for a bicycle. Aluminum conducts heat at roughly 200 Watts per meter-Kelvin (W/m·K), while conventional plastics struggle along at 0.3 W/m·K, a 600-fold performance chasm. 

Yet the proliferation of electronics in automotive and even aerospace vehicles demands thermal management solutions that aluminum increasingly cannot provide: complex geometries with integrated features, electrical isolation without secondary coatings, resistance to galvanic corrosion and high pH environments and, of course, the need for substantially lower mass. 

Thermally conductive polymers (TCP) offer a solution, but previous attempts created materials so highly filled with conductive particles that they behaved more like brittle ceramics than processable thermoplastics, defeating the purpose entirely.

Sentherm (Belfast, Northern Ireland, U.K.) approaches this contradiction differently. Rather than simply maximizing filler content to chase aluminum’s thermal conductivity, the company is leaning into the fact that heat transfer in real components doesn’t scale linearly with material conductivity. 

“A formulation achieving 1.5-3.0 W/m·K, still far below aluminum, can match or exceed the overall system thermal performance when the material’s anisotropic properties are exploited through thoughtful part design and the polymer’s inherent advantages are fully leveraged,” notes Findhan Strain, Sentherm’s CTO. “This systems approach, whereby formulation, compounding, processing and part geometry are considered as interdependent variables rather than isolated parameters, forms the foundation of Sentherm’s technology.”

 

Multiscale thermal bridging

The core of Sentherm’s product lies in the interaction between conductive particles, such as graphene and graphite, within the polymer matrix, and customizing that interaction for specific applications using comprehensive material science knowledge. Graphite flakes, typically 1-100 microns in size, provide bulk thermal pathways. But gaps inevitably exist between these micron-scale particles, creating thermal bottlenecks. Graphene’s role is more subtle: Its nanoscale thickness, combined with lateral dimensions in the sub-micron to several-micron range, allows it to infiltrate the voids between graphite particles, bridging gaps from tens of nanometers up to several micrometers.

Think of it like building a highway system. Graphite creates the major routes, but without connecting roads between them, traffic stalls at every junction. Graphene provides those connections. With in-plane thermal conductivity reaching 2,000-4,000 W/m·K, graphene sheets dramatically increase the effective contact area between adjacent graphite flakes while reducing thermal boundary resistance at their interfaces. This multiscale architecture creates continuous 2D and 3D conductive networks that achieve significantly higher effective thermal conductivity than graphite alone.

“The aspect ratios and geometries of these conductive fillers interact during compounding in ways that aren’t immediately obvious,” explains Strain. “Highly conductive fillers, like graphene, allow it to conform and bridge, but you have to control shear forces carefully. Too much shear during compounding breaks large flakes into finer pieces. Too little, and you don’t achieve homogeneous dispersion. We balance all this with application-specific additives.”

The company has two patents published and in review covering graphene-graphite polymer combinations at various ratios and graphene with aluminum nitride (AlN). The latter presents an interesting trade-off: AlN offers excellent intrinsic thermal conductivity (170-200 W/m·K) but introduces ceramic brittleness. Sentherm’s approach builds conductive networks at lower total ceramic volume fractions by using hybrid fillers, where plate-like fillers can deflect cracks. This allows them to hit target conductivities of 5-10 W/m·K with less AlN, hence less embrittlement.

The crystallinity paradox

Metals like aluminum are highly thermally conductive thanks to their crystallinity or lattice structure, providing an ordered atomic architecture that facilitates efficient energy transport via both free electrons and lattice vibrations (phonons). Think of aluminum’s internal structure like a well-organized city with two delivery systems working simultaneously. The atoms are arranged in neat, orderly rows, like terrace houses on a grid of streets. When one end gets hot, heat travels through this city in two ways.

First, you've got free electrons zipping around like motorcycles weaving through traffic. These electrons aren't stuck to any particular atom; they're free to roam. When one side heats up, these electron-motorcycles speed toward the cool side, carrying energy with them. It's fast and efficient because the orderly streets let them move without constantly bumping into obstacles.

Second, the atoms themselves start shaking. Picture each atom as a person standing in that orderly grid, and when one person gets jostled, they bump into their neighbor, who bumps into their neighbor, and so on, like a wave traveling through a crowd. These vibrations (physicists call them phonons, but really they're just coordinated shaking) pass energy down the line.

The orderly arrangement is crucial for thermal energy transfer. It's the difference between passing a bucket of water down a neat line of firefighters versus trying to do it through a mosh pit. In aluminum's crystalline structure, both the electron-motorcycles and the atom-vibrations can travel efficiently because everything's lined up properly. That's why metals conduct heat so well.

Early in development of their TCP, Sentherm observed something unexpected. Polymer crystallinity displayed a non-monotonic relationship with actual thermal conductivity performance. In other words, they aren’t consistently linear, but actually have a V-shaped correlation. As crystallinity increases from low levels, thermal conductivity initially improves as expected, but beyond an optimal point, it plateaus and then declines.

“The interface between crystalline and amorphous phases creates an abrupt change in order, stiffness, density and vibrational properties,” explains Dr. Beatriz Mayoral, Sentherm’s polymer lead. “These interfaces can act as phonon scattering sites. Below the optimal crystallinity, you’re gaining structured pathways for heat transfer. Above it, you’re multiplying interfacial boundaries that disrupt phonon transport.”

This relationship is influenced by various factors, including cooling rates, how fillers act as nucleating agents and polymer chemistry variations between suppliers. Two manufacturers producing nominally identical nylon 6 (PA6) can yield notably different thermal performance in the same formulation. “We encountered instances where certain polymers performed exceptionally well, while chemically similar materials from different manufacturers yielded poor results,” notes Strain. “Much of Sentherm’s formulation work involves mapping these interactions. We’re not just selecting a polymer grade, but understanding which specific manufacturer’s material, processed under what conditions, produces optimal filler distribution and crystallinity.”

The team also discovered that moisture and processing volatiles create performance degradation that thermogravimetric analysis doesn’t always reveal. “Even with neutralized and dried additives, problems can persist,” Strain acknowledges. “Low bulk density fillers can harbor embedded volatiles that are difficult to fully remove. Polymer degradation sometimes occurs earlier than anticipated, potentially through enhanced melt conductivity but more likely due to residual contaminants. Controlling these parameters is vital to achieve desired performance.”

 

Process-dependent anisotropy

The manufacturing method also dramatically affects filler orientation and thus thermal performance. Injection molding exposes the melted polymer to high shear rates and fountain flow, which strongly aligns anisotropic fillers parallel to flow direction and mold surfaces. This enhances in-plane conductivity but disrupts through-thickness pathways. Compression molding, by contrast, involves minimal shear and mainly through-thickness compaction. Fillers retain more random vertical orientation, enabling better particle-to-particle contact across the thickness. Sustained pressure also reduces voids and improves packing density.

The result is that identical formulations show markedly different thermal behavior, so the manufacturing route is critical to understand the application. It is somewhat known within the industry that different processes will result in different properties. Therefore, tailoring the formulation and design with the processing method to achieve the optimal outcome is crucial. Many of Sentherm’s formulations exhibit in-plane conductivity three to five times higher than through-thickness values, even though through-thickness performance remains strong. “This anisotropy isn’t a limitation if you design for it,” Strain emphasizes. “We use computer-aided design and topology optimization software to design and manufacture for routing heat along high-conductivity axes, incorporating ribbing and other features typical in polymer heat exchange parts.”

Perhaps surprising is that thermoforming, which involves biaxial stretching of filled polymer sheets, actually enhances conductivity rather than degrading it. During stretching, filler particles physically align along the stretch direction. “The electrical conductivity of particles becomes directionally dependent under stress,” explains Mayoral, whose Ph.D. research on carbon nanotubes informed this understanding. “Stretching improves dispersion and reduces interparticle distances, strengthening the conductive network.” One flexible PE formulation achieved 1.5-1.6 W/m·K through-thickness conductivity after extrusion and thermoforming while maintaining considerable drapability.

This behavior extends to the polymer matrix itself. The polymer chains themselves respond to stretching by aligning along the strain direction, similar to how pulling a tangled rope straightens individual fibers. This molecular alignment increases the polymer's own thermal conductivity in that direction while simultaneously creating oriented channels between filler particles that reduce thermal boundary resistance. The stretched matrix essentially becomes a more thermally transparent medium that allows the filler network to function more efficiently than in the randomly oriented as-molded state.

 

Compounding as a critical variable

Sentherm also discovered that identical formulations processed at different compounding facilities yield different properties. A formulation compounded in U.K. versus Central Europe, for instance, produces measurably different thermal conductivity despite identical recipes. The differences stem from screw design, residence time distribution, temperature profiles in feeding versus metering zones, shear intensity, drying conditions, volatile extraction efficiency and the sequence and timing of filler introduction.

“This is as much about knowing the processing characteristics of your supply chain and adjusting formulations accordingly as it is about the base recipe,” Strain notes. “High shear compounding, versus medium shear, affects how fillers disperse, which some polymers tolerate and others do not. Temperature control impacts polymer flow and additive distribution. It’s akin to traditional thermoset composites where every step contributes to finished properties.”

This reality shapes Sentherm’s business model. Rather than simply selling pellets, the company offers an end-to-end solution: assessing thermal requirements, arriving at both part and formulation designs, then producing the polymer and manufacturing the component. “We feel a systematic approach is needed for successful outcomes,” Strain explains. “It’s similar to when customers consider using carbon or glass fiber composites instead of aluminum. Designing a ‘black metal’ is suboptimal.”

Chip cooling validation

A straightforward test case demonstrates this integrated approach. Sentherm used a chip dissipating 5 watts of electrical energy into heat, and positioned it beneath various heat sinks — passive heat exchangers commonly used to cool automotive electronic devices — measuring maximum chip temperature to represent thermal management efficacy. An aluminum reference heat sink weighing 206.5 grams achieved 46.3°C nominal chip temperature. A standard polymer heat sink of similar geometry reduced weight to 95.6 grams but failed thermally, reaching 148.2°C. A version using Sentherm’s thermally conductive polymer with no design optimization stood at 99.4 grams and achieved 55.2°C. Finally, Sentherm’s thermally conductive polymer, combined with design for material and accounting for anisotropic heat transfer, came in at 159.9 grams and achieved 46.9°C — nearly matching aluminum performance with a 29% weight reduction. 

This progression reveals truly significant improvement relies on more than thermal conductivity alone. For example, going from 0.3 W/m·K to 1.0 W/m·K provides enormous benefits, while moving further from 1.5 W/m·K to 3.0 W/m·K offers only incremental improvement. Beyond a certain threshold, additional conductivity provides minimal performance gain. “According to Fourier’s law, thermal conductivity is proportional to heat transfer,” Strain observes. “In reality, there’s much more to it, and above certain points, there’s a law of diminishing returns.”

Sentherm bridges the remaining gap through anisotropic property exploitation and enhanced surface area via component design. In the case above, the polymer’s lower density (1,200-1,600 kg/m³) compared to aluminum (2,700 kg/m³) allows for adding material volume without excessive weight penalty. Complex fin geometries, internal ribbing and variable wall thicknesses — features difficult or impossible in cast aluminum — redistribute heat from concentrated sources to larger dissipation areas producing similar chip temperatures. However, this case study of a chip heat exchanger design wasn’t fully optimized, suggesting even further weight reductions are achievable.

Strain cautions that the thermal mass difference between polymers and aluminum also affects transient response. Although the specific heat capacity of Sentherm’s formulations better suits thermal cycling than conventional polymers, whether this benefits or hinders performance depends on application specifics. For intermittent high-power pulses, he explains, the response characteristics differ from aluminum in ways that require design consideration rather than simple material substitution.

Automotive industry integration

Modern vehicles contain 1,000-3,500 semiconductor devices, with electric vehicles typically exceeding internal combustion vehicles. Not all require active cooling, but power electronics, motor drives, battery management systems and ADAS processors — perhaps 20-100 cooled chips per vehicle — create substantial thermal management demands. Power densities vary, but a typical scenario might involve a 48 × 43-millimeter chip (20.6 square centimeters) dissipating 5-50 watts.

Battery pack assemblies present another opportunity. Sentherm has developed battery spacers that transfer heat from cells to coolant plates. Switching from aluminum to thermally conductive polymer achieves up to 30% weight reduction in the overall assembly. For one automotive application, material costs increased by 1.5 times compared to aluminum, but assembly time decreased significantly. The overall installed part cost dropped to 80% of baseline with a 24% weight reduction, all with a conservative design  similar to the aluminum reference part.

The assembly advantages Sentherm’s approach offers extend beyond simple part consolidation. Polymer processing allows molding screw bosses, snap-fit features, locating pins and alignment surfaces directly into thermal management components. These integrated features eliminate separate fasteners and reduce assembly labor. Electrical isolation, which is critical in high-voltage battery systems, comes inherent to the material rather than requiring secondary coating operations.

Sentherm offers two TCP classes for these cases: an electrically conductive (typically carbon-based, 1,200-1,300 kg/m³, lower cost) and electrically isolating (ceramic-filled, 1,500-1,600 kg/m³, slightly higher cost). The choice depends on whether the application requires ground paths or isolation. Hybrid architectures are also possible, with surface electrical conductivity differing from internal properties.

Durability,circularity, carbon footprint

Automotive thermal management components experience continuous temperature swings — from below freezing to operating temperatures exceeding a range of 100°C thousands of times over a vehicle's service life. Unlike homogeneous aluminum, filled polymer composites face a fundamental durability challenge during these cycles: the filler particles and polymer matrix expand at different rates, creating interfacial stresses that can degrade performance over time.

Thermal cycling creates differential expansion between filler and matrix, potentially causing interface degradation over time. The magnitude depends on load, temperature range, cycle count, environmental factors, filler arrangement and base polymer selection. To address this, Sentherm prioritizes interfacial adhesion through compatible filler-matrix chemistry and formulation design that maintains acceptable flexibility despite high filler loading. Most of its formulations achieve strain-at-break values exceeding 1.5%, substantially better than competing TCP. Remaining anticipated degradation can be addressed via engineering safety factors.

From a circular economy perspective, Sentherm’s TCP can be reground and reprocessed, though with important limitations:

• Multiple extrusion passes induce some degradation, but don’t prevent reuse.
• Degradation magnitude depends on processing severity and base polymer characteristics.
• Aggressive processing or poor drying increases property loss.

“As with most end-of-life elements, the main issue is whether someone will actually recover the material rather than landfilling it,” Strain notes. “If it’s recovered, we certainly can reprocess it.”

Meanwhile, with respect to embodied carbon, TCP offers substantial advantages. An independent assessment by Studio Fieschi (Turin, Italy) compared aluminum heat exchanger fins to TCP variants with enhanced surface area and comparable thermal performance. Even assuming 50% recycled aluminum content in a European supply chain and worst-case landfilling for the TCP part, the polymer showed 82.1% lower embodied carbon due to much lower production energy requirements.

Expanding material envelope

Sentherm recently achieved UL 94 V-0 fire retardancy classification while maintaining 2 W/m·K through-thickness conductivity in a PA6 formulation. “The material flows well during processing and isn’t excessively brittle, contradicting the assumption that fire retardants must compromise thermal or mechanical performance,” Strain explains. “Certain fire retardants behave better than others from a conductivity perspective, so we’ve extensively tested formulations to minimize thermal conductivity impact.”

The company works across polymer families from PPA and PPS to PA6, PA66 and polyphenylene oxide blends. Near-term development focuses on incorporating long fiber reinforcement through compression molding or overmolding. In a TCP case, short fibers provide many small, disconnected heat-flow paths whereas long fibers form more continuous networks, improving heat transfer along fiber length while the matrix-filler system handles transverse thermal transport. Processing methods will differ as long fiber composites suit compression molding rather than injection molding, but the approach could deliver enhanced mechanical properties alongside optimized thermal management.

“TCP are for industries where lower mass, assembly benefits, design freedom and corrosion resistance matter as much as thermal performance,” Strain highlights. “We’re not trying to make polymers behave exactly like aluminum. We’re creating solutions aluminum can’t provide.”