Rain gear waterproof ratings — what do they really mean?

Understanding Rain Gear Ratings

When shopping for rain gear, you’ll often come across various waterproof ratings, such as 5,000 mm, 10,000 mm, or 20,000 mm. These numbers represent the garment’s resistance to water penetration, as measured in millimeters using standardized tests like the ISO 811 or AATCC 42. In these tests, a column of water is sprayed onto the garment under increasing pressure until it penetrates through the fabric. The higher the rating, the greater the pressure required to penetrate the fabric.

Choosing the Right Rain Gear for Hypothermia Risk

In the Pacific Northwest, where wet cold conditions persist year-round, choosing the right rain gear is crucial to prevent hypothermia. For most activities, a rain jacket with a waterproof rating of 10,000 mm or higher is recommended. This rating provides adequate protection against moderate to heavy rain, common in the region. However, for high-risk activities, such as kayaking or hiking in heavy downpours, consider a garment with a higher rating, such as 20,000 mm or more.

Factors Affecting Rain Gear Performance

While waterproof ratings provide a general indication of a garment’s performance, various factors can affect its actual performance in the field. These include garment quality, fit, and maintenance. A well-made garment with a good fit and proper maintenance will outperform a cheaper, poorly made option. Additionally, wind, temperature, and humidity can compromise the garment’s waterproofness, even with a high rating. To maximize rain gear performance, ensure a snug fit, use a breathable base layer, and maintain your gear regularly.