【Haichuan Black Technology】What’s it like to wear polyimide, a rocket insulation material?

Cross-sector cutting-edge technology: Rocket engine materials used in clothing. What would it be like to use the key materials from rocket engines in clothes? This sounds like a plot from a science fiction movie, but it is now gradually becoming a reality. The key material mentioned here is polyimide; many people may hear this name for the first time, but it has long been a \"star material\" in high-end industrial fields. This material possesses extremely high strength; it can be used to manufacture components for body armor, as well as to produce lightweight and strong carbon fiber oriented fibers. As one of the three key polymer materials that pose barriers to the development of high-tech industries in our country, polyimide has remained relatively under the radar. The reason it is rarely seen in the public eye is that its primary application areas are in extreme environmental conditions. CCTV News has reported on cases related to the development of rocket engines in China, stating that the nozzles of these engines must be made from materials with exceptional heat resistance in order to withstand the extremely high temperatures of thousands of degrees Celsius during launches, and polyimide is the preferred material for such purposes.

Its extremely low thermal conductivity is the key advantage of polyimide; this property enables it to function stably in extreme high-temperature environments, and it also lays the foundation for its application in the clothing industry – as the main requirement for keeping warm in winter is to prevent heat loss. How impressive is the thermal insulation performance of polyimides? There is a classic comparative test in the industry: polyimide high-temperature tape and ordinary tape are applied to solder respectively, and then heated directly with a spray gun. The test results are clear: the exposed solder and the solder covered with ordinary tape melted due to heat within just a few seconds ； The solder covered by the polyimide tape remained completely intact, as heat simply could not penetrate the material to reach it. Thanks to this exceptional heat-insulating property, polyimide has become an ideal material for filling winter warm clothing; it is no longer the exclusive \"industrial elite\" reserved for rocket engines, and is now making its way into ordinary people’s wardrobes.

The drawbacks of traditional cotton jackets: it’s difficult to achieve both warmth and lightness. In the cotton jackets available on the market today, the insulation filling is mostly made of polyester fibers. The principle behind the insulation provided by this material is simple: it relies on the three-dimensional, fluffy structure of the filling to trap air, and it uses the low thermal conductivity of air to prevent heat loss. To improve warmth retention, the conventional approach in this industry is to use finer polyester fibers; the finer the fibers, the more air they can retain, and theoretically, this leads to better insulation. However, this approach actually involves two difficult-to-overcome issues. The first potential issue is the heat conduction properties of the fibers themselves. The thermal conductivity of polyester fiber is 0.084. Although this value seems low, it still presents significant shortcomings in terms of insulation; some heat escapes directly along the fibers themselves, resulting in a reduced actual insulating effect. The second potential problem is insufficient structural stability. Although ultra-fine polyester fibers have a higher degree of fluffiness, their strength is reduced as well, making them more prone to compression. A review of winter clothing published by China Consumer News found that many jackets labeled as \"high-quality technical cotton\" actually became flatter the more they were worn. Many consumers have also reported that for high-end polyester cotton jackets such as those with a gold label, the thermal resistance test results claimed by manufacturers are quite high, but the actual warmth provided when worn is far from as good as those test figures suggest. The core issue lies in compression deformation: the fluffy structure made of ultra-fine polyester fibers collapses rapidly under the pressure exerted by daily activities, resulting in a significant reduction in the amount of air stored, and thus a decline in its insulating properties. This is the core problem with traditional cotton coats: to keep warm, more fibers need to be used, which makes the coat bulky and heavy ； For portability, the amount of fiber filling is reduced, which results in insufficient insulation; it seems that achieving both warmth and lightness is a contradictory goal that’s difficult to satisfy.

A breakthrough for polyimide: precisely solving the key challenges related to warmth retention. The fleeces made from polyimide material effectively address the two main shortcomings of traditional polyester-based winter jackets. What it offers is not just an improvement in warmth retention, but rather a rethinking of the principles behind warmth retention in winter clothing. First and foremost, there is the advancement in terms of thermal conductivity. The thermal conductivity of polyimide is as low as 0.03, a value that is extremely close to that of air. This means that it hardly transfers heat on its own, and together with the trapped air, it creates a dual insulation barrier. In comparison, the thermal conductivity of polyester fiber at 0.084 is significantly lower than that of polyimide; garments filled with polyimide can easily outperform traditional cotton jackets in terms of heat retention, even when the amount of filling used is less. Next is the advantage of structural stability. Polyimide has a higher elastic modulus, a property that has been verified in industrial applications; foam pieces made from it are less compressible than those made from ultra-fine polyester fibers, at the same level of fluffiness. Industry evaluation data show that after being subjected to multiple extrusion deformations, polyimide fluff can quickly return to its fluffy state, with its air-storage structure remaining stable. This addresses the common problem of traditional cotton jackets becoming flatter over time, ensuring that their insulating performance stays consistent for a long period. However, the widespread adoption of polyimide clothing still faces challenges. It has long been a niche industrial material, with very low awareness among the general public. Companies that wish to promote such products need to invest a great deal of effort in educating the market, so that consumers can understand the value of using rocket materials in clothing.