Carbon nanotube-based film achieves record-low thermal conductivity at extreme temperatures, offering ultralight, scalable insulation for aerospace, energy, and high-temperature industrial applications.
(Nanowerk Spotlight) As spacecraft reenter Earth’s atmosphere, their surfaces endure temperatures hotter than molten lava. Hypersonic vehicles, high-efficiency jet engines, and next-generation reactors all face similar thermal extremes. Protecting these systems from destructive heat requires insulation that can block not just conduction through solids and gases but also radiation, the most difficult mode of heat transfer to suppress at high temperatures.
Yet nearly every material used for this purpose falters under the demands of weight, stability, and temperature range. Many insulators work well at moderate heat but fail when temperatures exceed 1500 °C. Others can survive the heat but conduct too much of it. Even the most advanced ceramic composites or graphite-based foams face tradeoffs that have, so far, proven hard to overcome.
Despite decades of research, the ideal high-temperature thermal insulator remains elusive. The goal is simple: a material that resists all forms of heat transfer, remains stable at thousands of degrees, and adds minimal weight. The difficulty lies in the physics. At extreme temperatures, heat behaves less like something that flows and more like something that escapes through photons, vibrating atoms, and gas molecules. Stopping it requires not just bulk insulation but precise control over how heat carriers interact with a material’s internal structure.
Efforts to control these interactions at the nanoscale have opened new possibilities. Carbon-based nanomaterials such as graphene and carbon nanotubes are better known for their high thermal conductivity, but their behavior changes dramatically when engineered into porous, aligned, and layered assemblies.
Under the right conditions, the same structures that once carried heat efficiently can be tuned to trap and block it. The challenge is building such structures at meaningful scales and proving they work across a realistic temperature range.
In a study published in Advanced Functional Materials (“Carbon Nanostructure–Enabled High‐Performance Thermal Insulation for Extreme‐Temperature Application”), researchers from Tsinghua University report a material that does just that. Developed from super-aligned carbon nanotube films stacked into multilayered structures (SACNT-SF), the material combines low density, nanometer-scale thickness, and a highly porous architecture to achieve thermal insulation performance that surpasses conventional materials at both ambient and extreme conditions.
Most notably, it remains effective up to 2600 °C in vacuum and 3000 °C in inert gas while maintaining one of the lowest thermal conductivities ever recorded for an insulation material. The discovery, made during the construction of a high-temperature furnace, now offers a practical route toward scalable, flexible, and ultralight insulation systems for environments where traditional materials reach their limits.
SACNT-SF achieves effective thermal conductivities as low as 0.004 watts per meter kelvin at room temperature and just 0.03 watts per meter kelvin at 2600 °C. These values are significantly lower than those reported for conventional insulation materials. For example, graphite felt, a widely used insulator in high-temperature applications, has a thermal conductivity around 1.6 watts per meter kelvin at the same elevated temperature.
SACNT array, film, and stacked film. a) Drawing a SACNT film from a SACNT array on a 290 mm × 140 mm quartz substrate. b) SEM image of a single-layer SACNT film. c) Schematic illustration showing the fabrication of SACNT-SF by either winding SACNT film on a rod or stacking multiple SACNT films together. d) SEM images of different sections of SACNT-SF, the scale bar is 20 μm. e) SACNT-SF with dimensions of 40 mm × 50 mm and a thickness of 2 mm. f) A SACNT-SF fabricated by winding SACNT film on a copper cylinder. g) Photograph of drawing a 550 mm-wide SACNT film from a SACNT array. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
To understand how SACNT-SF performs so well, the researchers analyzed how it resists each mode of heat transfer. The carbon nanotubes in the films are aligned along the plane of the film, while heat flows across the thickness of the stack. This arrangement reduces the speed at which vibrations or phonons can move through the solid structure. Since the individual nanotubes are just 10 to 20 nanometers wide, and the films are full of voids, the amount of material available to conduct heat is very small. The porous structure also makes it harder for gas molecules to move around inside, suppressing heat transfer by diffusion.
In gaseous environments, heat can also move via molecular collisions. This effect becomes less important when the pores in a material are small enough that gas molecules bounce off solid walls more often than they hit each other, a phenomenon known as the Knudsen effect. Because the carbon nanotubes are so small and closely spaced, SACNT-SF enters this regime even at atmospheric pressure, making it especially effective as an insulator in air or argon.
At high temperatures, radiative heat transfer, or energy carried by photons, becomes a major factor. Unlike solid or gas conduction, this form of heat transfer can occur even in vacuum. SACNT-SF addresses this by absorbing and scattering incoming radiation. Carbon in the sp² configuration, found in nanotubes and graphene, is naturally very effective at blocking infrared radiation.
This is enhanced by the complex internal structure of the films and the electronic properties of the nanotubes themselves. In particular, carbon nanotubes exhibit electronic states known as van Hove singularities, which increase their interaction with light over a wide range of wavelengths relevant to thermal radiation.
The researchers found that SACNT-SF effectively traps thermal photons within the material, greatly reducing radiative conductivity. They also showed that the degree of photon absorption depends on how the nanotubes are aligned relative to the direction and polarization of incoming radiation. By stacking layers at varying angles rather than in parallel they could further suppress radiative heat transfer.
Importantly, SACNT-SF retains its insulation properties at extreme temperatures. It remains stable up to 2600 °C in vacuum and 3000 °C in an inert gas atmosphere. In air, it begins to oxidize at around 500 °C, but unlike some carbon materials, it does not ignite or continue burning once removed from flame. After 310 thermal cycles between room temperature and 2000 °C, the material lost less than five percent of its thermal resistance. This suggests good long-term stability under demanding conditions.
Mechanically, SACNT films are flexible and lightweight, with densities ranging from 5 to 100 kilograms per cubic meter. They can be wrapped around objects of various shapes, making them suitable for irregular surfaces. Although the films are not rigid, they have adequate tensile strength for many uses, ranging from about 1 to 60 megapascals depending on density and orientation. These values hold up reasonably well even at high temperatures.
To further improve performance, the researchers explored how adjusting the material’s density and the alignment of layers could optimize insulation. Increasing the density can reduce radiative and gas-phase conduction, though it comes with a tradeoff of slightly higher solid-phase conductivity. They calculated and confirmed that the best results occur when layers are oriented at angles to each other and packed at a density that balances all three heat transfer paths.
The simplicity of the fabrication process is also noteworthy. SACNT films can be drawn continuously from vertically grown nanotube arrays and stacked or wound into large-area formats. The researchers have already produced films up to 550 millimeters wide and hundreds of meters long, indicating potential scalability.
Continuous drawing of a super-aligned carbon nanotube film several meters long from a vertically aligned CNT array.
The study demonstrates how nanoscale engineering, combined with careful control over structure and orientation, can produce materials with performance characteristics not achievable by traditional means. By suppressing solid, gas, and radiative heat transfer simultaneously, SACNT-SF sets a new benchmark for lightweight, high-temperature insulation. Applications could range from aerospace and fusion reactors to industrial kilns and thermal shielding in electronics.
Future developments may focus on surface treatments or coatings to protect SACNT-SF in oxygen-rich environments, allowing it to perform even in open-air conditions. Techniques such as atomic layer deposition or chemical vapor infiltration could make this possible without compromising the material’s core properties.
If this article was useful, support our independent nanotechnology reporting with any amount.
Your contribution funds the next explainer and keeps Nanowerk open for everyone.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
