## 1 Introduction  
Aerogel was developed by [PERSON] in 1931 [1] and is, presently, known to man, the lightest solid in the world [2]. It is produced by replacing the liquid component of a gel with a gas to create a nano-porous solid, which, from an initial monolithic form, can then be converted to a granular form [3]. It possesses a remarkably low thermal conductivity [4] that is lower than those of other commercial insulation materials [5, 6, 7], as well as air [8, 9, 10, 11]. It efficiently prevents solid and gaseous conduction by virtue of its non-crystalline slender skeleton and distinctive nano-sized pore structure. Accordingly, it has been labeled as a superinsulation material [12, 13, 14]. It can be synthesized from many types of materials, such as, among others, alumina, carbon, polymer, and silica [15]. Silica aerogel possesses an ultra-low thermal conductivity of 0.005 W/mK due to its high specific surface area of 500-1200 m\({}^{2}\)/g, high porosity of 80-99.8%, and low density of about 0.003 g/cm\({}^{3}\) by virtue of its nano-structure [16, 17, 18, 19, 20]. It has a fractal geometry that can be structured randomly in colloidal aggregate systems. In general, its synthesis is performed in three steps, which are, preparation, aging, and drying, of silica gel. The preparation of silica gel is performed by adding a catalyst to a silica source solution to induce gelation as a result of the condensation of the liquid phase. The gel is then aged in its mother solution to increase its strength and, as a consequence, minimize the amount of shrinkage during the next step, where drying is performed at a slow rate under the conditions of supercritical drying to extricate the gel from the pore liquid without disintegrating its solid matrix, which, in the case of the conventional evaporation, will occur due to capillary action [4; 20]. Aerogel can be manufactured in monolithic or granular forms [3]. In general, monolithic aerogel has better thermal and optical properties than granular aerogel [21; 22]. However, monolithic aerogel has been found to be fragile [23] and, consequently, susceptible to cracking during manufacturing [24]. Large-scale commercialization of monolithic aerogel is not yet actualized owing to its fragility, as well as limitations in manufacturing technology [25]. Apart from that, monolithic aerogel is expensive and requires protection from moisture and tension [21; 22]. Hence, in view of the impediment to the manufacturing and application of monolithic aerogel, the adoption of aerogel in commercial products is predominantly, at present, in its granular form [21; 22; 25]. By virtue of its ultra-low thermal conductivity, aerogel has been employed as the insulation material for the space suits of the National Aeronautics and Space Administration of USA, underwater oil pipelines and the metallurgy industry [26]. Typically, owing to the fragility of monolithic aerogel, the development and production of aerogel-based insulation materials involve the incorporation of granular aerogel with other materials to form composite materials that can be employed as insulation materials for various applications where heat transfer is a concern. Installation of an aerogel-based insulation material in the building envelope has been explored in previous research, where the material has to concurrently fulfill thermal and strength performance requirements. The prospect of employing aerogel in the building envelope was tested for the first time in [PERSON] et al. [26], where the thermal performance of residential steel- and wood-framed walls and commercial low-sloped roofs that were insulated with a fiber-reinforced silica aerogel composite material were evaluated using three-dimensional computer simulations and a series of hot-box tests. Later, [PERSON] et al.