MDF (Medium Density Fibre) board is a commonly used particle board. Moisture Resistant MDF is used in places with high humidity levels. In comparison to standard MDF, Moisture Resistant MDF (or MR MDF) contains a moisture-repellent resin which gives it a better moisture resistant rating. However, MR MDF shouldn't be mistaken to be water resistant as it's still prone to swelling and warping if in direct contact with such elements. MR is a unique moisture resistant panel which can be used in a greater variety of applications than standard MDF