Fiber aerogel, as the lightest material, has set a new record and possesses unique properties, heralding a future transformation in materials. With its outstanding lightweight quality, fiber aerogel has become the lightest material in the world today. This innovative achievement not only breaks the records in materials science but also indicates that a new chapter in the field of materials is about to unfold. This lightweight and highly unique material is expected to bring revolutionary changes in multiple fields. 
When it comes to the concept of "gel", you might think of jelly, aloe vera gel or contact lenses. However, these are just some manifestations of gel in daily life. In the field of science, gel is defined as the colloidal particles in a sol or solution, which form an elastic solid with a spatial network structure under the action of the dispersing medium. Specifically, when the dispersing medium is a gas, it is called an aerogel; and if water is used as the dispersing medium, it is called a hydrogel. 
Aerogel, a material composed mainly of air, is remarkable for its extremely low density, with over 98% of the space occupied by air, making it the solid with the lowest density in the world. Additionally, it is also a type of nanomaterial, exhibiting unique physical and chemical properties. Recently, the nanofiber research team from Donghua University, in their latest paper published in 2015, introduced a lightweight and elastic fiber aerogel that they developed. After undergoing China's metrological certification, the solid material density of this fiber aerogel is only 0.12 milligrams per cubic centimeter. This achievement not only broke the density record previously held by "all-carbon aerogel" (0.16 milligrams per cubic centimeter), but also made it claim the title of "the world's lightest material". 
❒ The Third Generation Aerogel Materials
Cellulose aerogel is regarded as the third-generation material due to its environmental friendliness and multi-functionality, and it has great potential for wide applications. The transition from fossil fuels and excessive emissions of harmful gases has had a profound impact on the environment and resources, which has further driven the development of natural polymer materials towards sustainability, biodegradability, and resource utilization. Among various natural polymers, cellulose has attracted much attention due to its abundant reserves on Earth. The research and development of cellulose materials and their derivatives not only meet the strategic requirements of sustainable development but also demonstrate broad application prospects. 
Among them, cellulose aerogel, as an important branch of cellulose materials, thanks to its characteristics such as renewability, biodegradability, ease of surface modification, high porosity, high specific surface area, and low density, has constructed a 3D interconnected porous network structure, becoming a highly environmentally friendly multi-functional material. It has demonstrated outstanding application potential in various fields such as adsorption and separation, insulation, biomedicine, energy storage, as well as metal nanoparticles/metal oxide carriers and catalysis, and is thus hailed as the "third-generation aerogel material". 
❒ Classification of Cellulose Aerogels
The classification of cellulose aerogels is into nano, regenerated, and derivative aerogels. Different sources and properties lead to diverse application options. When discussing the potential applications of cellulose aerogels, it is inevitable that we need to understand their classification. Based on different preparation methods and properties, cellulose aerogels can be divided into various types. These classifications not only help us gain a deeper understanding of the diversity of this material but also provide more choices for practical applications. Next, we will delve into several main classifications of cellulose aerogels. 
Cellulose, this remarkable substance found in nature, is derived from various sources. It exists in plant-based cellulose materials such as straw, cotton, and wood, and can also be extracted through bacterial fermentation, for example, by acetic acid bacteria. Additionally, recycled cellulose from waste materials, such as newspapers and cardboard boxes, also provides the possibility for the preparation of cellulose aerogels. Based on these different sources and structural characteristics, cellulose aerogels can be further classified into three categories: nanocellulose aerogels, recycled cellulose aerogels, and cellulose derivative aerogels. 
❒ Nanofiberized Cellulose Aerogel
Nanofiberized Cellulose Aerogel (NC) is composed of nanofiber cellulose materials with diameters ranging from 2 to 100 nm and lengths of several hundred nanometers or micrometers. It is prepared by methods such as solvent method, mechanical dispersion method, or dissolution and dispersion with organic solvent derivatives. Subsequently, a hydrogel is formed through cross-linking reactions, and then dried to obtain cellulose aerogel. 
❒ Regenerated Cellulose Aerogel
The preparation process of regenerated cellulose aerogel involves four key steps. Firstly, cellulose is completely dissolved in an appropriate solvent; secondly, it is regenerated through solvent exchange; then, a hydrogel is formed through gelation treatment; finally, after drying, the regenerated cellulose aerogel is obtained. 
Regenerated cellulose aerogel differs from other aerogels due to its larger average pore size and usually over 30% shrinkage rate. During its preparation process, methods such as acid hydrolysis, enzymatic treatment, or mechanical disintegration are commonly used to extract regenerated cellulose. This aerogel has become a subject of extensive research due to its simple production process and low cost. 
❒ Cellulose derivative aerogels
Chemical modification of cellulose aerogels is a crucial step in preparing cellulose derivative aerogels. These aerogels not only have low density and high porosity, but also exhibit excellent thermal conductivity and dimensional stability. Depending on specific application requirements, appropriate chemical modification can further enhance or optimize the original properties of the cellulose aerogels.