Waterproof and Breathability Ratings Explained

Waterproof, breathable outerwear has come a long way in recent years. Look in any gear store and you can choose from a variety of clothing that is made to preform out in rain, snow, wind and sleet. For any outdoor activity, you want clothing that is going to keep you warm and dry. Manufacturers attach different numerical ratings to their products to help customers determine the best choice for their desired activities and weather conditions. This guide aims to explain waterproof and breathability ratings to help you make sense of all those numbers and determine which piece of outerwear is best for you.

Measuring Waterproof Ratings

The outdoor industry determines waterproof ratings based on a water column test. This test measures water permeability under pressure. Water permeability is a measure of how water flows through a porous material. Considering pressure is an important part of the water column test because it affects how water soaks through fabric. Your ski pants may keep snow out when you’re standing still, but become damp when pressures is added by sitting on the chairlift.

In the water column test, a one-inch-diameter column of water is placed over the fabric in question for a period of 24 hours. The millimeter rating comes from how high you can fill the column before any water gets through the fabric in the allotted 24-hour time period.

Waterproofing Ratings Explained

Below are the waterproof ratings used for outdoor clothing:

• Less than 5,000 mm/24 hours
  • Lightly water-resistant. It is misleading when a manufacturer advertises a waterproof rating this low.
  • This fabric will protect you from mist, or a one-time light splash.
  • Avoid if you are looking for prolonged moisture protection.
• 5,000 mm (often written as ‘5K waterproof’)
  • Water-resistant; stands up to light rain and dry snow under no pressure.
  • This is great for an everyday rain jacket around town and light activity.
• 10,000 mm (10 K)
  • Somewhat waterproof; stands up to moderate rain and average snow under light pressure.
• 15,000 mm (15K)
  • Waterproof; stands up to moderate rain and snow under moderate pressure.
  • Great baseline protection for skiing, hiking and outdoor activities.
• 20,000 mm (20K)
  • Very waterproof; stands up to heavy rain and wet snow under heavy pressure
  • Avid recreators, this is what you want for serious rain protection!
  • Great for storm skiing, camping, and anytime you’re active in wet and windy conditions.
• More than 20,000 mm
  • Maximum water protection under very heavy pressure; this is like what garbage bags and rain boots are rated.
  • This is what you want for expeditions and extreme conditions where staying dry is a matter of safety.

Measuring Breathability

Wearing waterproof gear helps keep you dry from external moisture, but what about internal moisture? When you’re active and working up a sweat, good airflow ensures heat and moisture can escape and won’t keep you damp. Similar to waterproof treatments, manufacturers utilize a variety of different technologies to get moisture out in high-performance fabrics. They all involve a large pore membrane that lets water vapor out, without letting liquid water in.

There is not an industry standard to test the transfer rate of water vapor, or what we refer to as breathability. And even if there was, several uncontrollable variables like temperature and humidity affect the water vapor transfer rate, making it difficult to standardize.

Breathability is often reported in terms of the amount of water vapor, in grams, that can pass through a square meter of a material for 24 hours (g/m2).

Breathability Ratings Explained

Here are the breathability ratings for outdoor clothing:

• 5,000 g/m2 or less
  • Slightly breathable; not much perspiration can get through this material.
  • Undesirable for any true activity, if it gets exposed to moisture it will probably stay damp and be uncomfortable.
• 10,000 g/mm2
  • Breathable enough for moderate activity.
  • Provides baseline breathability for running, hiking and working out.
  • Moisture is able to evaporate during activity and the fabric is able to dry out.
• 20,000 g/mm2
  • Very breathable, allows water vapor to escape so you don’t get sticky when you’re working up a sweat.
  • Great for high aerobic activity like skiing, trail-running, mountaineering and climbing where the fabric gets wet but easily dries even after consistent exposure to moisture.
  • Ideal for multi-day expeditions when you’re wearing the same thing each day.

Now that you’re a bit familiarized with waterproof and breathability ratings, you can determine the right outerwear for you. Knowing that you want a 15K waterproof ski jacket or pants with a breathability rating over 10,000 g/mm2 helps you narrow down your options. From there you’ve got something concrete to search for on the web or ask retail associates for help.

Applying Knowledge

If waterproof and breathability ratings still look like a jumble of numbers to you, don’t worry. These ratings are there to help you, the customer, gage how different garments perform out in the elements. By no means do you need to be an expert on technical gear in order to recreate successfully in the outdoors. To keep it simple when choosing technical clothing, ask yourself these questions:

• What kind of protection do you need?
  • If staying dry is a non-negotiable for you then you know to look for something with a waterproof rating of at least 15K. If you’re concerned about overheating, even when moisture is in the air, then you know to look for options with breathability ratings of 20,000 g/mm2 or more to maximize ventilation and comfort.
• What are you going to be doing?
  • Because waterproof ratings are based on how the fabric protects under pressure, it’s important to consider what you’ll be doing in the garment. If you’re backpacking or powder skiing, you’ll need heavy pressure protection over 20K that performs with a backpack on through deep snow or bush whacking through trees.
• What are the conditions/weather?
  • In any outdoor activity, it is best to plan for the unexpected and always bring a waterproof layer– even if there’s no moisture in the forecast. If you have a dedicated outdoor activity, look for outerwear that is going to preform best in the “typical” conditions. For example, trail runners will want a waterproof and super breathable lightweight option that packs well and doesn’t trap heat. Resort skiers want something that is warm and super waterproof even in a blizzard.

Acknowledging Progress: PFA-Free Technology

It wouldn’t be a complete discussion on technical outerwear without touching on PFAS. A recent milestone in the outdoor industry is the phasing out of per- and poly-fluoroalkyl substances (PFAS) from outdoor products. Specifically, the technology that makes outerwear waterproof and breathable. For years, the chemicals used in these protective treatments contained PFAS, often called “forever chemicals,” which have proven to be harmful and cause serious health conditions. Thanks to advancements in technology, manufacturers are taking the lead in producing PFA-free technical gear that is just as waterproof and breathable as the former technology. To learn more about PFAS and PFA-free outerwear, read our PFAS in Outdoor Clothing post.

A reliable waterproof jacket is a staple on any recreator’s gear list. Even if you only ski or hike a few times a year, weather can be unpredictable in the mountains. Staying warm and dry is crucial for managing risk during activities. A basic understanding of waterproof and breathability ratings in outerwear gives you the power to find the best technical clothing to keep you warm and dry for all your adventures.

By Jans Experts

Additional Links

How to Layer for Alpine Skiing

Hardshells and Softshells: What’s the Difference?