Declaration water column: the water column is a unit of the tightness of technical fabrics such as provide functional and rain gear. may be the case that using the water column (measuring cylinder which is filled with water) indicated the amount of water that weigh on the fabric before to pass through this moisture, nearly 1,000 mm of water column pressure correspond to 1 kg / dm ³. From a strictly defined value (1.300 mm rain gear), the tissue is considered to be waterproof.