## 2 Materials and Methods  
The pore densities of reticulated porous ceramics that can be easily obtained in experiments are generally limited to approximately 45 PPI. Therefore, the studies mentioned above mostly focused on reticulated porous ceramics with pore densities of less than 45 PPI. For example, reticulated porous ceramics prepared from various raw materials such as aluminum nitride (20 PPI) [10], alumina-zirconia composite (20 PPI) [37], alumina (5 PPI [38] and 20 PPI [4; 39; 40]), zirconia (45 PPI) [7], silicon carbide (8 PPI [5] and 10 PPI [6]), silicon nitride (10 PPI) [18], mullite (20 PPI) [8], and cordierite (10 PPI) [11] had pore density values lower than 45 PPI. In this study, the target pore density of the reticulated porous diatomite-kaolin composite was 80 PPI. This is because the compressive strength of a reticulated porous diatomite-kaolin composite with pore density of 45 PPI would be too low to enable its application, owing to the inherent porous and irregular nature of diatomic particles, despite being composited with kaolin. As the pore density value exceeds 80 PPI, optimizing the viscosity of the ceramic slurry becomes highly important to enable its penetration inside the sacrificial polymer template (a low viscosity being advantageous for this purpose) and completely coat the strut walls of the template (which is facilitated by high viscosity). The average particle size as well as solid loading, binder, and dispersant are the key properties of slurry compositions that affect the viscosity of a ceramic slurry. Numerous studies have been reported, including on alumina slurries (high solid loading and low viscosity for micro-droplet jetting) [41], alumina magnesia silicate slurries (high solid loading and low viscosity for additive manufacturing) [42], magnesium aluminate spinel slurries (high solid loading and low viscosity for slip casting) [43], zirconia-toughened alumina slurries (high solid loading and low viscosity for additive manufacturing) [44], ceramic ink (appropriate solid loading and suitable viscosity for inkjet printing) [45], and cerium oxide slurries (high solid loading and low viscosity for dip-coating) [46]. In order to prepare a reticulated porous ceramic, a high solid loading and a moderate viscosity are required: (1) if the solid loading of the ceramic slurry is too low, the densification of the strut walls will be insufficient (in other words, the porosity of the strut walls of the reticulated porous ceramic will be too high), resulting in a low compressive strength; (2) if the viscosity of the ceramic slurry is too high, it is difficult for it to completely fill the internal pores of the sacrificial polymer template. It is also very difficult to remove the excessive ceramic slurry while maintaining the formation of thin and uniform ceramic coatings over the strut walls of the sacrificial polymer template; (3) if the viscosity of the ceramic slurry is too low, it will not be sufficient to firmly coat the strut walls of the sacrificial polymer template, as a result, an increasing number of defects can be induced by the uncoated strut wall because of the low adhesion, severely degrading the compressive strength of reticulated porous ceramics. Generally, the viscosity of the ceramic slurry increased sharply with increasing solid loading and decreased with increasing particle size. Therefore, to obtain a high solid loading diatomite-kaolin composite slurry with moderate viscosity, we tried to identify the optimal composition with the appropriate amount and average size of diatomite-kaolin composite particles. Although a slightly higher solid loading might be achieved by surface modification [47; 48], we decided to leave this challenge for a future study.