Aerogel is a porous material, also known as solid smoke or solid haze. It has a very high specific surface area and porosity, and there are a large number of tiny pores in its structure. These pores make aerogels have excellent adsorption capacity and thermal insulation properties, so they are widely used in construction, chemical industry, aviation and other fields.
In fact, aerogels usually have a very low density, less dense than air, between 0.001 and 0.5 g/cm³, while air has a density of about 1.2 kg/m³. This means that the same volume of aerogel is much lighter than air. However, such a low density aerogel can not float in the air, what is the reason for this?
Just because aerogel is less dense than air doesn't mean it will fly. This is because density is simply the ratio of an object's mass to its volume, and whether an object rises also needs to take into account other factors such as gravity and buoyancy.

According to Archimedes' principle, the buoyancy of an object in a liquid or gas is equal to the weight of the liquid or gas it displaces. When the density of an object is less than the density of the surrounding medium, such as air, it will experience an upward buoyancy force. Aerogel in the microscopic sense is a bunch of skeleton material with branches connected to each other and supporting each other, with a lot of voids in between. The density of the skeleton itself is greater than the air, which is equivalent to a large number of skeleton materials dispersed and immersed in the air, so the aerogel cannot float up.
In addition, although the density of the aerogel is small, it is still subject to the gravity of the Earth to keep it on the ground. The aerogel will not float up on its own initiative unless it is given sufficient lift, such as by using an external device or encasing it in an air bag. So although aerogel is less dense than air, it doesn't float on its own. Aerogel materials have the characteristics of low density, low thermal conductivity, high specific surface area, shock absorption and sound absorption, chemical stability, etc., and are widely used in construction, petrochemical, transportation, power plants and other fields of fire insulation.