In recent years, aerogel, as a new type of material, has been hailed as "the world's lightest solid material" and has become highly sought after in the materials market. But what exactly is aerogel? It actually originates from gel substances. Gel refers to an elastic semi-solid substance that contains a large amount of liquid and maintains a certain shape. Common gel substances in daily life include tofu, jelly, fever-reducing patches, the pearls in bubble tea, and aloe vera gel with skin care effects.
If the liquid components in a gel are successfully replaced with air or gas while maintaining the original solid structure of the gel, then this new solid substance is aerogel - a nano-porous material mainly composed of nano-scale solid skeletons. In 1931, American scientist Samuel Stephens Kistler successfully prepared aerogel for the first time. He used supercritical drying technology to prepare a loose and porous amorphous solid material with high specific surface area, low bulk density, and low thermal conductivity, and named it "aerogel". Kistler published this achievement, "Polymer Diffusion Aerogels and Jellies", in the journal Nature, marking the birth of aerogel materials. The term "aerogel" in English, where "aero" means "air" and "gel" means "gel", vividly describes the characteristic of this material being filled with air and having a nano-porous structure.
This article mainly introduces pure aerogel materials, that is, aerogel without composite reinforcing fibers. Pure aerogel is a nano-material and has the following significant properties: 
1) High porosity: The internal porosity of aerogels can reach up to 99.8%. This high porosity endows aerogels with an enormous specific surface area, which is conducive to adsorption and catalytic reactions. 
2) Extremely low density: Aerogels have an extremely low density and are very lightweight. The density of most aerogels typically ranges from 3 to 50 kg/m³, and they are often referred to as "frozen smoke." The density of all-carbon aerogels can be as low as 0.16 kg/m³, which is less than one-seventh the density of air. 
3) High specific surface area: The nano-scale framework and pore structure endow it with an extremely high specific surface area, reaching up to 2000 m²/g, exhibiting a super sponge-like adsorption effect. 
4) Excellent thermal insulation performance: Due to its high porosity and low density, aerogel has an extremely low thermal conductivity, typically ranging from 0.013 to 0.02 W/(m·K), which is much lower than that of most traditional insulation materials, making it suitable for thermal insulation requirements in extreme environments. 
5) Excellent sound insulation effect: The porous structure of aerogel can effectively absorb sound waves and reduce noise transmission, making it suitable for applications where sound insulation is required. 
6) Chemical stability: Many aerogel materials have good resistance to acids, bases, and organic solvents. For instance, inorganic aerogels exhibit excellent chemical stability at high temperatures. 
7) Other unique properties: such as optical properties, electrical properties, etc. 
Based on supercritical, atmospheric pressure and vacuum freeze-drying technologies, many materials can be made into pure aerogel materials, such as polyurethane, silica, alumina, etc. Pure aerogel materials have developed into a large family with a wide variety of types. You can browse the next knowledge article "Main Classification Methods of Pure Aerogel Materials" for more information.
It should be noted here that pure aerogels are currently all prepared in laboratories and have not yet achieved industrial-scale production. They usually need to be used in combination with other materials to improve their strength and practicality. Most of the aerogels sold on the market are silica aerogel composite insulation materials, which actually have some obvious differences from pure aerogel materials in terms of characteristics. 
The thermal insulation application of aerogels has been developed most extensively. Through vacuum impregnation of fiber reinforcement technology and drying treatment techniques, organic, inorganic and hybrid composite aerogel materials are highly suitable for thermal insulation fields. Among them, inorganic silica aerogel composite materials are the main type, usually made into blankets or boards, and are called "aerogel composite insulation materials". However, it should be noted that "aerogel composite insulation materials" and "composite aerogels" are two different concepts.