Hard Fire Brick. If you want a fire brick to hold up for a long time, this is a great choice. These fire bricks are not meant to drill or shape due to the density. I use them to control the heat and size of the opening on my gas forge. This is not considered an insulating fire brick and is not ideal for reflecting heat. The advantage to these bricks is the high heat tolerance and longevity.
Manufactured by Harbison Walker.