Oven bricks actually have higher thermal capacity than steel/iron, but much lower conductivity. Steel or iron in a 450C oven would burn the bottom of the pizza

Oven bricks actually have higher thermal capacity than steel/iron, but much lower conductivity. Steel or iron in a 450C oven would burn the bottom of the pizza before the top was anywhere close to done. It works well in home ovens at much lower temperatures (say 250C).