The client renders the world's bricks. The way it renders these bricks will vary depending on what the brick is or how it was modified. The client's use of “fast bricks” refers to the brick rendering method designed for rendering complex or rapidly changing bricks.

Bricks are usually rendered in clusters. A brick is rendered as a fast brick under the following conditions:

• The brick's shape is set non-default.
• The brick's properties which affect its rendering were changed after creation.
• The brick was explicitly defined as a fast brick on creation.

Fast bricks address the performance issue of regenerating world chunks after a brick was changed. This however comes with its own performance issues. Fast bricks are rendered one-by-one in the client unlike bricks in a cluster. In most situations, it isn't ideal to use fast bricks in a way that is mostly static.