From the insulation layer of Mars probes to the stealth coating of fighter jets, and to the battery thermal management of new energy vehicles, as well as the insulation of industrial pipelines, in recent years, this remarkable material that once existed only in laboratories - aerogel - is gradually leaving the laboratory and being applied on a large scale in fields such as aerospace, industry, new energy, construction, and environmental protection. It is called "the lightest solid in the world", also known as "solid air", and is even hailed as "the magical material that changes the world". Many people are curious: What exactly is aerogel? Why is it called "solid air"? What are its amazing properties? Why is it an indispensable core new material in the aerospace and industrial fields? What changes has it brought to our lives? 
Many people have a perception that aerogel is just a new type of insulation material, similar to the common foam plastic and rock wool, with only a slightly better insulation effect. However, in fact, aerogel is a solid material with a nano-porous structure. More than 90% of its interior is air, and the highest can reach 99.8%. That is to say, this solid material is almost entirely composed of air, which is why it is called "solid air". It is currently the solid material with the lowest density known to humanity. The lightest aerogel has a density of only 0.16 milligrams per cubic centimeter, which is even lighter than air. At the same time, it also possesses unparalleled performance that no other materials can match. It has disruptive advantages in areas such as heat insulation, sound insulation, adsorption, and catalysis, and is one of the most promising new nano materials in the 21st century. 
The advent of aerogels actually has a history of nearly a hundred years. As early as 1931, American scientist Kistler successfully prepared the world's first silicon aerogel through supercritical drying technology, confirming the existence of this "solid material with all its interior being pores". However, in the following decades, the preparation cost of aerogels was extremely high and the process was extremely complex. Only a small amount could be prepared in the laboratory and could not be mass-produced, which could only be used in some cutting-edge scientific research fields and did not achieve widespread application. It was not until the past few decades that with the continuous advancement of material technology, the preparation process of aerogels was continuously optimized, the cost was significantly reduced, and industrial production was gradually realized. It began to be widely applied in various fields and has become a popular track in the field of new materials. 
The reason why aerogel is called a "magical material" lies in its unique nano-porous structure, which brings unparalleled performance that no other materials can match. Inside the aerogel, there is a three-dimensional network structure formed by the interconnection of nano-sized colloidal particles. Between the networks are countless nano-sized pores, with the pore size ranging from 2 to 50 nanometers. It is precisely this unique structure that gives it a series of revolutionary properties. 
First and most well-known is the extremely high insulation and heat preservation performance. Aerogel is currently the solid material with the best insulation performance known to humanity. We all know that heat transfer mainly occurs through three ways: heat conduction, heat convection, and heat radiation. The nano-porous structure of aerogel can simultaneously inhibit these three heat transfer methods, achieving the ultimate insulation effect. 
Firstly, in terms of heat conduction, the solid framework of the aerogel is at the nanoscale, and the path for heat transfer within the solid framework is infinitely elongated, resulting in extremely low heat conduction efficiency. At the same time, the pore sizes inside the aerogel are smaller than the average free path of air molecules, and air molecules cannot freely move within the pores, making it almost impossible for them to transfer heat through collisions with air molecules, completely inhibiting the heat conduction of air. Secondly, in terms of heat convection, the pores inside the aerogel are all closed and at the nanoscale. Air cannot flow within the pores and thus cannot form heat convection, and therefore cannot transfer heat. Thirdly, in terms of heat radiation, by adding a small amount of shading agents to the aerogel, it can effectively suppress infrared heat radiation and further enhance the insulation performance. 
It is precisely because of these characteristics that the thermal conductivity of aerogel can be as low as 0.013W/(m・K) or even lower, lower than still-moving air. It is currently the solid material with the lowest thermal conductivity. We can use an intuitive example to appreciate its heat insulation performance: a 1-centimeter-thick aerogel insulation board. Its heat insulation effect is equivalent to 20-30 ordinary glass sheets, or 30 centimeters thick rock wool insulation board. Even if one side of it is heated by a blowtorch flame to over 1000 degrees Celsius, when touched on the other side with your hand, it still only feels warm. Even under the protection of aerogel, a match can be lit on the other side of it without igniting the paper towel. This extreme heat insulation performance is unmatched by any other insulation material. 
The second core performance is its extremely low density and extremely high specific surface area. The density of aerogel can reach as low as 0.16 milligrams per cubic centimeter, making it lighter than air. It can even be placed on a flower without bending its petals. It is currently the lightest solid known to humanity. At the same time, it has countless nanometer-sized pores inside, with a specific surface area of over 1000 square meters per gram. That means, when all the pores of 1 gram of aerogel are expanded, the area would be as large as a football field. This unique combination of ultra-lightweight and high specific surface area gives it great potential for applications in areas such as adsorption, catalysis, and energy storage. 
The third core performance is excellent sound insulation and absorption capabilities. The three-dimensional nano-porous structure of aerogel can effectively absorb and attenuate sound waves. For mid and high-frequency sound waves, the sound absorption coefficient can reach over 90%. At the same time, it has an extremely low density and is extremely lightweight, making it an excellent lightweight sound insulation material. It can be used in fields such as construction, automobiles, aerospace, etc. for sound insulation and noise reduction. 
The fourth core performance is excellent fire resistance and flame retardancy. The mainstream silica aerogel is an inorganic non-metallic material that is non-flammable and resistant to high temperatures. Its melting point can reach above 1200 degrees Celsius, and it does not release toxic gases at high temperatures. It is an A-class fire-resistant material and can also provide insulation, perfectly meeting the fire protection requirements in fields such as construction, industry, and aerospace. 
In addition, aerogels also possess excellent chemical stability, corrosion resistance, and aging resistance. They can operate stably in extreme conditions such as strong acids, strong bases, high temperatures, and high humidity for a long time, with a service life of up to several decades, far exceeding that of traditional insulation materials. 
It is precisely because of these exceptional properties that aerogels have first been widely applied in the aerospace field and have become an indispensable core material in aerospace engineering. In the aerospace field, spacecraft need to face extremely extreme temperature environments. On the sunny side of the spacecraft, the temperature can reach above 100 degrees Celsius, while on the shady side, the temperature can drop to below -100 degrees Celsius. The precise instruments of the probes need to work in a stable temperature environment, which requires an extremely high-performance insulation and heat preservation material. Whether it is the Mars probe of the United States, the space shuttle, or China's Shenzhou spacecraft, Tianwen-1 Mars probe, and Chang'e lunar probe, all of them have adopted aerogel as the core insulation and heat preservation material. It can ensure the normal operation of the instruments inside the probe in extreme temperature environments. At the same time, its ultra-lightweight characteristic can also significantly reduce the weight of the spacecraft and lower the launch cost. 
Apart from the aerospace field, today's aerogels have achieved large-scale application in the industrial sector and have become the core material for industrial energy conservation. In industries such as petrochemicals, power, and metallurgy, there are numerous high-temperature pipelines, industrial kilns, and storage tank equipment. Traditional insulation materials, such as rock wool and silicagel cotton, have poor insulation performance, short service life, and are prone to absorbing water and powdering, requiring frequent replacement, resulting in significant energy waste and maintenance costs. However, aerogel insulation materials have 3-5 times the insulation performance of traditional materials. With the same insulation effect, the thickness required is only one-third of that of traditional materials. At the same time, their service life lasts for more than 15 years, do not require frequent replacement, and are waterproof and corrosion-resistant, which can significantly reduce the heat loss of pipelines and equipment and improve energy utilization efficiency. According to calculations, using aerogel insulation materials can reduce the heat loss of industrial pipelines by more than 70%. For high-energy-consuming industries, this can bring huge energy-saving benefits and economic benefits, and is the core material for achieving carbon neutrality in the industrial sector. 
In the field of new energy, aerogel has also become an indispensable key material. The most critical safety issue of today's new energy vehicles is the thermal runaway of the power battery. Once the battery undergoes thermal runaway, the temperature will rise rapidly and even cause fire or explosion. However, the ultimate heat insulation performance of aerogel can perfectly solve this problem. In the power battery pack, using aerogel insulation sheets to separate different cells and modules can effectively prevent the transfer of heat and avoid the spread of thermal runaway to the entire battery pack, significantly improving the safety of the power battery. At the same time, aerogel can also be used for the thermal management of batteries, providing insulation in low-temperature environments to prevent battery range reduction; in high-temperature environments, it can provide heat insulation to ensure that the battery operates within an appropriate temperature range and extend the battery's service life. In addition to new energy vehicles, aerogel can also be used in new energy fields such as photovoltaic, wind power, and energy storage stations, playing the roles of heat insulation, heat preservation, and fire prevention, and promoting the development of the new energy industry. 
In the field of architecture, aerogel is also bringing about a revolution in building energy conservation. China's building energy consumption accounts for more than one-third of the country's total energy consumption. The insulation and heat preservation performance of buildings is the core factor determining building energy consumption. Traditional building insulation materials, such as polystyrene boards and rock wool, either have poor insulation performance or fail to meet fire safety standards, and they are thick, occupying indoor space. However, aerogel insulation materials have 3 to 5 times the insulation performance of traditional materials. With only 1 centimeter of thickness, they can achieve the insulation effect of 5 centimeters of traditional materials. Moreover, they are A-level fireproof materials, non-flammable, heat-resistant, waterproof, soundproof, and resistant to aging, perfectly suitable for building exterior insulation, interior insulation, and window and door insulation scenarios. They can significantly reduce the heating and cooling energy consumption of buildings and achieve building energy conservation, making them the core material for achieving carbon neutrality in the construction sector. 
In addition, aerogel can be used as an efficient adsorption material in the field of environmental protection to treat industrial wastewater and exhaust gas, adsorb heavy metals and organic pollutants in water, and remove harmful gases such as formaldehyde and VOCs from the air. In the clothing industry, it can be made into ultra-thin thermal insulation fabrics. With a thickness of only a few millimeters, it can achieve the same thermal insulation effect as traditional down jackets with several centimeters of thickness, completely changing the design of outdoor clothing and cold-weather wear. In the military field, it can be used as a stealth coating for fighter jets and ships, as well as individual cold protection equipment and explosion-proof equipment, with extremely broad application prospects. 
Of course, the large-scale application of aerogels still faces some challenges. The most crucial one is the cost issue. Although the production cost of aerogels has significantly decreased in recent years, it is still higher than that of traditional insulation materials, which leads to low willingness for their application in many fields. Secondly, traditional silica aerogels are brittle and have poor toughness, making them prone to powdering and limiting their application in some scenarios. To address this, they need to be modified through composite methods to enhance their mechanical properties. However, with the continuous advancement of preparation technologies, the cost of aerogels is rapidly decreasing, and modification technologies are constantly breaking through. These problems are being gradually resolved. 
In the field of aerogels, our country has already taken the lead globally. Whether it is the preparation technology, production capacity, or the expansion of application scenarios, we rank first worldwide. We have formed a complete industrial chain from raw materials, preparation equipment, to product production and engineering application, breaking the technological monopoly of foreign countries. The cost of aerogels has also dropped to the lowest level globally, and we are promoting the large-scale popularization of aerogel materials. 
From the novel materials in the laboratory to their wide application in aerospace, industry, new energy, construction and other fields, the development of aerogels has spanned nearly a century. This mysterious material, known as "solid air", with its extraordinary properties, is transforming various industries and driving energy conservation, carbon reduction, and technological innovation. In the future, with the continuous advancement of material technology, aerogels will surely permeate every aspect of our lives, bringing us more surprises and becoming the core new material driving the sustainable development of human society.