In flooring installation, a damp proof membrane (often referred to as a DPM) is where a barrier is put between the floor and the subfloor to either stop or slow the evaporation of water from the sub floor.
DPMs can be physical e.g. polythene sheets or special underlays, or chemical, where a liquid DPM is rolled onto the floor to form a water barrier.
DPMs are commonly used underneath flooring which will be damaged by moisture, including LVT, wood or laminate floors. Before installation, your flooring installer may check the moisture levels in your subfloor to determine whether you require a damp proof membrane, or which type you need.
DPMs are especially used with concrete subfloors, as these can hold very large levels of moisture and can take many months, even years, to fully dry.