Waterproofing in a tent shows us how much water the outer fabric can repel. It is measured in millimeters (mm) and refers to how many millimeters of vertical water column (and therefore pressure) a square centimeter of fabric can withstand without being penetrated by water. The higher the degree of waterproofing, the less breathable the fabric is, and therefore the warmer the tent. Widely accepted waterproofing values range from 500mm to 10000mm. Theoretically, any fabric with waterproofing >1000mm is characterized as waterproof. For example, a summer tent may have waterproofing from 500 to 1500mm.