Drainage Gravel 20mmConsisting of a crushed blue metal screened to a 20mm size, our drainage gravel is a versatile stone used for civil, commercial and residential purposes. This sizing of drainage gravel is used for applications such as trench drainage, retaining wall drainage and even pathways and driveways. Drainage Gravel Benefits Durable and resistant to weather Heat Absorption qualities Great at diverting water Resistant to erosion (less upkeep in the future) For