The “mm of waterproofness” on a winter coat refers to the water column measurement used to assess the water resistance of the fabric. This is an indication of the coat's ability to repel water before it begins to penetrate.
The higher the number of millimeters (mm), the more waterproof the coat. The measurement is based on the material's ability to withstand water pressure without allowing moisture to penetrate.
It is important to note that, in addition to mm of waterproofing, other factors such as seam design, zippers and water-repellent treatments can also affect the overall ability of the coat to remain waterproof.
