For various reasons it might be necessary to make materials waterproof, meaning it is impossible for water to seep into the material. To check whether something is waterproof, a water column test is applied. The material is tested using a column or tube, which is filled with a number of millimetres of water. The more water there is in the column, and the more millimetres of water there are, the higher the pressure on the material. So this test looks at the number of millimetres of water that a material or fabric can withstand per m². Depending on the application, a lower or higher water column value is required.