The BLOOM Pour Over Coffee Brewer is crafted of food-grade stainless steel so you don’t have to preheat, and to facilitate a micro-filter for even extraction. With ceramic, you need to pre-heat or the ceramic will absorb the heat, and your coffee will lose a substantial amount of heat. With metal, you can pre-heat, but it is not necessary. Metal has low thermal capacity, and we chose the thickness of the metal to retain the most heat for best flavor.