Why is slate commonly used for the bed of a billiards table?

Slate is the preferred material for the bed of a billiards table primarily because of its physical properties as a metamorphic rock.

When quarried and processed, slate can be split into slabs that possess great tensile strength and durability, allowing it to maintain a perfectly flat, stable surface over time. Unlike wood or other materials that might warp or sag due to humidity or temperature changes, high-quality slate provides a rigid, level foundation essential for the precision required in billiards. Its ability to be finished with smooth, even surfaces ensures that the billiard cloth can be stretched tightly and uniformly across the table, facilitating consistent ball roll.1