Aerogel is a solid material composed of a nano-porous network structure formed by the aggregation of colloidal particles or polymer molecules. The pores are filled with gaseous dispersed media, and both the solid phase and the pore structure are at the nanoscale. 
Aerogel is hailed as one of the least dense solids in the world, with a density of only 3.0 kg/m³, approximately 2.75 times that of air. Hence, it is named "frozen smoke". Its microscopic structure exhibits a distinctive "honeycomb-like" porous morphology, endowing it with the following core characteristics: 
Large specific surface area: Nanometer-sized pores provide an extremely large contact area
High porosity: Usually over 90%
Extremely low density: Much lower than traditional insulation materials
Very low thermal conductivity: At room temperature, it can be lower than 0.023 W/(m·K)
Synthesis process of aerogels
The preparation of aerogels generally goes through two key processes: sol-gel polymerization and supercritical drying. Among them, the sol-gel process mainly has three implementation methods: 
Gelation of colloidal powder sols
The gelation is formed by the hydrolysis and polycondensation of alcohol or nitrate precursors
The polymer monomers in the solution polymerize or copolymerize to form a gel
Composite aerogels: An engineering solution that takes advantage of strengths and mitigates weaknesses
Although pure aerogels are lightweight, have a high porosity, and have low thermal conductivity, their low strength and high brittleness limit their direct application in building exterior wall insulation. Therefore, in engineering practice, aerogels are usually combined with inorganic fibers and other materials to form aerogel composite products. 
The advantage of this combined strategy lies in: 
Maintain the ultra-low thermal conductivity, fire resistance and high-temperature stability of the aerogel itself
Make up for the shortcomings of poor mechanical properties and fragility of pure aerogel
Expand its practical application scenarios in construction engineering
At present, products mainly composed of SiO₂ aerogel composite materials are the most widely used in thermal engineering and are rapidly penetrating into the field of building insulation. 
Core Performance Analysis
Outstanding Thermal Insulation Performance
The thermal conductivity coefficient is the core parameter for evaluating the thermal insulation performance of insulation materials.
The reason why aerogel composite products can achieve such a low thermal conductivity is due to their three-layer heat suppression mechanism: 
Inhibiting heat conduction: The high-porosity and low-conductivity nano three-dimensional pore structure effectively blocks the heat conduction path.
Inhibiting heat convection: The pore size of 50-60 nanometers prevents the free movement of air molecules, significantly suppressing convective heat transfer.
Inhibiting heat radiation: The 1-millimeter-thick aerogel material contains tens of thousands of pore walls, and each layer of the pore wall can serve as a reflection and refraction surface for radiation, maximizing the blocking of radiation heat transfer.
It is worth noting that as the temperature rises, the increase in the thermal conductivity of aerogel composite products is much lower than that of other materials - the higher the temperature, the more prominent its insulation advantage. 
Engineering Value: When applied to building exterior insulation, roof insulation, or passive house projects, the aerogel composite products not only effectively prevent heat loss between indoors and outdoors, but also can reduce the thickness of the insulation layer and the area of laying, lowering the overall engineering cost. At the same time, they fundamentally solve the quality risks such as cracking, peeling, and detachment caused by excessive thickness of the insulation layer. 
Excellent combustion performance
With the implementation of mandatory energy-saving measures in buildings, the fire safety of exterior wall insulation materials has become a core issue of concern in the industry. In the event of a fire, insulation materials with poor combustion performance will significantly facilitate the spread of the fire vertically, posing serious safety hazards. 
The aerogel composite products demonstrate outstanding fire resistance performance, and the reasons for this are as follows: 
The reinforcing material is inorganic fibers: The reinforcing base material used in the composite is usually made of inorganic fibers and is inherently non-flammable.
The gas gel body is non-flammable: SiO₂ gas gel is an inorganic material and has natural fire-resistant properties.
The preparation process has no organic residues: In the sol-gel process for preparation, gas replaces the liquid phase in the gel, and the final product contains almost no flammable organic components.
Therefore, the gas gel composite products can meet the A-level non-flammable standard for building materials and is an ideal solution that combines insulation and fire resistance. 
High-temperature stability
The aerogel composite products also perform well in high-temperature environments: 
In environments below 600℃, the linear shrinkage rate is extremely small and can be almost negligible.
At high temperatures, the internal structure remains amorphous, without undergoing volume shrinkage, melting, sintering or degradation.
The high-temperature thermal conductivity is excellent, and the heat preservation effect is stable and long-lasting.
This characteristic makes aerogel composite products also have extensive application value in scenarios such as high-temperature industrial pipelines and thermal equipment insulation. 
Future Outlook
In the context of the increasing global energy shortage and the continuous advancement of China's "carbon neutrality" goals, the requirements for energy conservation and emission reduction in buildings are constantly rising. Although the current production cost of aerogel composite products is relatively high, their comprehensive performance in three aspects - heat insulation and preservation, fire safety, and high-temperature stability - perfectly align with the national energy conservation and emission reduction policy orientation. 
With continuous innovation in the industry, continuous optimization of production processes, and reduction in costs through large-scale production, aerogel composite insulation products will undoubtedly occupy an important position in the future building insulation field and become one of the key materials driving the green transformation of the construction industry.