Relatively speaking, red bricks are good, but now they are mostly autoclaved bricks, which are more environmentally friendly.

Red brick is a sintered building brick made of clay, shale and coal gangue. Which is manually or mechanically crushed, kneaded and molded, dried and fired with an oxidizing flame at about 900 degrees Celsius.

Autoclaved brick is made of fly ash or other slag or lime sand as raw materials, adding lime, gypsum and aggregate, and through the processes of blank making, press molding and efficient steam curing. Autoclaved brick is made by stirring, digesting and autoclaving the finished product in an autoclave at high temperature.