A bituminous membrane is a thin layer of water-tight material that is laid over a surface. This layer is continuous and does not allow water to pass through it. Its main purpose is to resist hydrostatic pressure exerted by moisture in the liquid state. Waterproofing membranes consist of waterproof plastic, rubber, or coated-fabric materials.

The materials are used in a system to prevent the ingress of water into foundations, roofs, walls, basements, buildings, bridges and structures when properly installed. Waterproofing membrane should be strong, flexible, tear-resistant and elastic so that it can stretch to cover cracks and also move with the building. If the membrane is to be exposed to the sun, then it should be UV stable. The membrane should be flexible enough to take any shape it is laid over, and be capable of turning up and over walls and other construction features.