Water column is usually measured in millimeters (mm) or centimeters (cm) and refers to the height of a column of water that a material can withstand before water begins to penetrate it. For example, if a material has a water column rating of 10,000 mm, it means it can withstand a column of water 10,000 mm high before it starts to leak. To determine the water column of a material, the fabric is placed under a column of water and the point at which water begins to penetrate is recorded. The higher the water column before penetration occurs, the better the material is at resisting water.

Simply put, a material with a 10,000 mm water column will only start letting water through when the pressure equals 10 meters of water placed above it.

Below is an explanation of different water column levels and what they mean:

10,000 mm water column:

This provides good protection for materials used in moderate rain and snowfall. Furniture covers with this rating can protect against regular rain showers and light snow. Bag’in Nordic and SunGuard have this water column certification.

15,000 mm water column:

A water column of 15,000 mm offers even better protection and is suitable for areas with frequent rain and moderate snowfall. Furniture will withstand more precipitation and remain reliable in most weather conditions.

20,000 mm water column:

This level is suitable for locations with heavy rain and significant snowfall. Furniture will stay dry and well protected even in demanding weather conditions.

25,000 mm water column:

This is a very high level of water resistance, ideal for areas with extremely heavy rain and large amounts of snow. Furniture will remain highly protected and withstand even the most challenging weather conditions. Bag’in Nordic have this water column certification.