A dimple board (or “drainage mat”) is a heavy-duty plastic membrane with raised “dimples” that create an air gap between the soil and your foundation wall. This gap acts as a “pressure relief valve,” allowing water to fall straight down to the footer drain rather than pressing against the concrete. At Basement Expert, we use dimple boards as part of our multi-layered exterior system. It’s a simple but brilliant engineering solution that eliminates hydrostatic pressure and ensures your liquid membrane barrier isn’t overwhelmed.