Paraffin wax is a popular phase change material (PCM) used in thermal energy storage and passive temperature regulation. Its ability to store large amounts of latent heat during melting and release it during solidification makes it attractive for solar heating, building cooling, and thermal management. One of its most critical properties in engineering and energy systems is its thermal conductivity: paraffin wax has relatively low thermal conductivity, which can slow heat transfer in practical systems. Understanding how paraffin wax conducts heat—especially in solid vs liquid states—is essential for optimising its performance in heat transfer and PCM applications.
This blog explores the thermal conductivity of paraffin wax, how it compares to other materials, and how engineers and researchers enhance its heat transfer performance without sacrificing energy storage capacity.
When people refer to paraffin separately from paraffin wax, they are often talking about liquid paraffin (paraffin oil). The thermal conductivity of liquid paraffin is typically in the range of about 0.13–0.18 W/m·K at room temperature, somewhat lower than many liquids and far lower than metals. In practice, both solid paraffin wax and liquid paraffin have relatively modest thermal conductivities compared to common engineering fluids (such as water or oils with special additives) and to solid metals.
Thermal conductivity varies depending on:
The thermal conductivity of paraffin wax is relatively low, typically ranging from 0.2 to 0.4 W/m·K in its solid state. The exact value depends on the wax grade, crystal structure, packing density, and temperature. As the temperature approaches the melting point, the crystalline order diminishes, and the conductivity can shift to a similar low range (often slightly lower in the liquid phase). Because paraffin wax is a weak conductor of heat, heat transfer in wax-heavy systems is usually conduction-dominated in the solid phase. It can become convection-assisted once the wax is molten.
Although paraffin wax is a poor conductor of heat compared to metals or ceramics, it is acceptable for applications where slow, controlled heat transfer is desired.
Heat transfer in paraffin wax during charging or discharging of a PCM depends on both conduction and latent heat effects. In the solid phase, heat must diffuse through the wax matrix, so thermal conductivity governs the rate. As melting occurs, latent heat dominates the energy exchange, which can slow the apparent rate of temperature change even as conduction continues.
In many practical TES designs, natural convection in the liquid wax enhances heat transfer during the molten phase, improving overall performance. Effective heat transfer in paraffin wax systems thus involves:
Due to its low thermal conductivity, paraffin wax is not ideal for rapid heat transfer. However, it excels in latent heat storage, absorbing and releasing large amounts of energy during phase transitions. This makes it valuable in:
Its ability to store heat without rapid conduction allows for gradual temperature regulation, rather than instant heat dissipation.
For PCM applications, the useful metric is the effective thermal conductivity of paraffin wax during phase change and its translation into thermal diffusivity (α = k/(ρ cp)). Typical values at room temperature place k in the ~0.15–0.25 W/m·K range for solid wax and ~0.13–0.18 W/m·K for liquid paraffin, with cp around 2–3 kJ/kg·K and ρ around 800–900 kg/m³. The resulting diffusivity is very low (on the order of 10^-7 m²/s), which explains why pure paraffin wax stores a large amount of energy (latent heat) but transfers heat slowly.
This low conductivity motivates the development of composite PCMs and structure-enhanced configurations to boost heat transfer without compromising energy storage capacity.
As a phase change material (PCM), paraffin wax is prized for its:
However, its low thermal conductivity limits the rate at which heat can be absorbed or released. This bottleneck affects the efficiency of PCM systems unless mitigated by design enhancements.
Paraffin wax is one member of a family of waxes used in PCM and insulation applications. Most natural and synthetic waxes have similar low thermal conductivity values in the solid state, typically in the 0.1–0.25 W/m·K range. In practice, the key differences among waxes come from their phase-change temperatures, latent heat capacities, and melting behaviour rather than significant differences in their intrinsic conductivities.
Here is a brief comparison:
| WAX TYPE | THERMAL CONDUCTIVITY (W/m·K) | NOTES |
| PARAFFIN WAX | 0.2–0.4 | Low, stable |
| BEESWAX | ~0.3 | Slightly higher, natural |
| MICROCRYSTALLINE WAX | ~0.2–0.3 | Similar to paraffin, more flexible |
| CARNAUBA WAX | ~0.4 | Higher melting point, harder |
Paraffin wax offers a balance of cost, stability, and latent heat capacity, but lags in conductivity.
Thermal conductivity drops significantly when paraffin wax melts:
Overall, solid paraffin is usually slightly more conductive than the liquid in many systems, but both are considered low-conductivity media compared with metals or highly engineered composites. Designers must account for this shift when modelling PCM systems or heat transfer applications.
The latent heat capacity of paraffin wax is high, but its intrinsic thermal conductivity is low. Researchers and engineers use several strategies to enhance heat transfer while preserving energy storage properties:
Incorporating these enhancements can raise the effective conductivity from the baseline ~0.15–0.25 W/m·K to well above 0.5 W/m·K and in some engineered composites even into the 1–2 W/m·K range or higher, depending on filler type, loading, and processing. The key is to achieve a percolating conductive network without severely compromising latent heat storage, phase-change temperature range, and mechanical stability.
Paraffin wax offers unique advantages as a phase-change material, but its low thermal conductivity poses challenges for high-performance heat transfer applications. Understanding the differences in thermal conductivity between solid and liquid paraffin, and comparing them with other waxes, helps engineers and formulators optimise paraffin wax-based systems and make informed decisions. By leveraging additives, structural enhancements, and innovative design, paraffin wax can be transformed into a highly effective thermal management material—especially in energy storage, electronics cooling, and building insulation.
In summary, understanding the thermal conductivity of paraffin wax and how it differs from that of liquid paraffin, along with methods to enhance conduction, is crucial for designing efficient thermal energy storage solutions and PCM-based cooling or heating systems. By carefully balancing conduction improvements with latent heat retention, paraffin wax can deliver reliable, energy-dense thermal management across a wide range of applications.
Whether you're developing PCM systems or optimising wax formulations, mastering paraffin wax heat transfer properties is key to unlocking its full potential.
