## 2 Materials and Methods  
As the sacrificial template, commercial polyurethane foams (SKB Tech, Korea) with 10, 25, 45, 60, and 85 PPI, and dimensions of 50 mm \(\times\) 50 mm \(\times\) 10 mm were used for the experiments. A batch of diatomite-kaolin slurry was manufactured to coat the polyurethane foam, which consisted of 100 g of diatomite (Celite 499, Celite Corp, Lompoc, CA, USA), 30 g of kaolin (Kaolin, Sigma-Aldrich, Darmstadt, Germany) as a strength enhancer, 250 mL of distilled water, 4 g of DARVAN C-N (Vanderbilt Minerals, Norwalk, CT, USA) as a dispersant, and 20 g of polyvinyl alcohol (PVA) as an organic binder (PVA 500, Junei Chemical Co., Tokyo, Japan). The mixed diatomite-kaolin slurry was ball-milled using alumina balls for 4 h. The reticulated porous diatomite-kaolin composite specimens were prepared by the replica method. While implementing the conventional replica method, a polyurethane foam specimen was initially soaked in a diatomite-kaolin slurry until its internal pores were saturated with diatomite-kaolin particles. Subsequently, the impregnated polyurethane foam specimen was squeezed to remove any excess diatomite-kaolin slurry, and to enable the formation of a thin diatomite-kaolin coating over the struts of the open-cell pore structure. Then the specimen was dried for 24 h at room temperature. The dried specimen was heat-treated at 400 \({}^{\circ}\)C for 1 h to burn off the binder, and subsequently sintered for 1 h at 1200 \({}^{\circ}\)C. After sintering, the material was transformed into reticulated porous diatomite-kaolin composite. For comparison, reticulated porous alumina specimens were also prepared. Because it was very difficult to compare \"the same material and different microstructure\" or \"different material and the same microstructure\". Introducing the diatomite particles to a reticulated porous ceramic, means that the microstructure will be unique which motivated the author to investigate the reticulated porous diatomite. Therefore, the authors compared characteristics the specimens between \"a conventional and typical reticulated porous ceramic (alumina) and a novel and unique reticulated porous ceramic (diatomite-kaolin composite)\" regardless of the difference of microstructure. Alumina slurry consisted of 130 g of \(\alpha\)-alumina (AKP-30, Sumitomo Chemical Co., Ltd., Tokyo, Japan), 100 mL of distilled water, 1.5 g of methyl cellulose serving as a thickening agent (Sigma-Aldrich, Darmstadt, Germany), 4 g of DARVAN C-N (Vanderbilt Minerals, Norwalk, CT, USA) serving as a dispersant, and 5 g of PVA serving as an organic binder (PVA 500, Junsei Chemical Co., Tokyo, Japan). The optimized alumina slurry composition was obtained only after adding the dispersant in the middle of experiments during this study. Therefore, the un-optimized alumina slurry condition did not include the essential dispersant. All other preparing procedures were the same, except for the sintering temperature, which was 1600 \({}^{\circ}\)C.  
The pore characteristics of the specimens were characterized using scanning electron microscopy (SEM, JSM-5800, JEOL, Tokyo, Japan) and mercury porosimetry (Autopore IV 9510, Micromerities, Norcross, GA, USA). The viscosity was measured using a rotational rheometer (Discovery HR-1, TA Instruments, New Castle, DE, USA) at 25 \({}^{\circ}\)C. The three-dimensional microstructure was investigated through \(\mu\)- computed tomography (CT) (XT H 160, Voxel size = 3 \(\mu\)m, Nikon, Tokyo, Japan). The compressive strengths of the reticulated porous diatomite specimens were measured with a fixture using an Instron 4206 (Instron, Norwood, MA, USA) testing system. For the compressive strength testing, specimens with dimensions of 20 mm \(\times\) 20 mm \(\times\) 20 mm were prepared. The dielectric breakdown strengths were measured using the standard test apparatus of dielectric breakdown voltage with a DC power supply (C180 30 KV 10 mA, KSC, Seoul, Korea).