Abstract: Both the fabrication methods and properties of cellulose aerogels and silica–cellulose aerogels are discussed in detail. A combination of an aerogel structure and recycled cellulose fibres from paper waste can be used to form an advanced material, called a recycled cellulose aerogel, which is cost-effective and a promising material for oil absorption. This chapter also focuses on the thermal properties, such as thermal conductivity and thermal stability, of the recycled cellulose aerogels and their silica composites for the heat insulation applications. This is the first time that the benchmark data on the thermal properties of recycled cellulose-based aerogels have been summarized. Protein-based aerogels, novel biodegradable and biocompatible materials for lightweight food engineering and life science applications, are also briefly discussed.