Water resistance ratings are given in millimeters (mm), which is the height of a column of water that the fabric can withstand before leaking. The higher the number, the better the waterproofing. For example, a fabric with a 10K rating can withstand a column of water 10,000 mm high before leaking. - Good - 5,000 - 10,000 mm waterproofing for light rain and snow. Most snow pants have at least this rating. - Better - 15,000 mm waterproofing for longer periods in moderate rain or snow. - Best - 15,000 - 20,000+ mm waterproofing for extended periods in heavy rain or snow. This is typically only found in technical outerwear designed for extreme conditions. Waterproofing is just one factor to consider when choosing snow pants. Others include insulation, breathability, and fit. Insulation helps keep you warm, while breathability prevents you from getting too hot and sweaty. Fit is important for comfort and mobility. When choosing snow pants, it's a good idea to consider what kinds of activities you'll be doing in them. If you're mostly going to be walking around in the snow, you don't need as much waterproofing or insulation as someone who plans to spend hours skiing or snowboarding.