Waterproof, Breathable, Windproof, Sun Protection
The outdoor industry throws lots of techy terms and numbers at consumers to prove how awesomely high performance its products are. But what does it all even mean? Here is probably a much more detailed answer to that question than you ever even wanted.
Water-Repellent, Water-Resistant, Waterproof
Many technical clothing items feature a durable water-repellent (DWR) finish, which causes water to bead up and roll off of the fabric surface. DWR treatments are used either alone or to boost the performance of another waterproofing technology.
For the most part, the outdoor industry refers to waterproofing based on a water column test that measures water permeability under pressure. Pressure is an important aspect of this measurement because the same ski pants that are keeping snow out when you’re standing still, may become damp when, for example, you put pressure on them by sitting on a chairlift, or on the ground.
In the water column test, a 1-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.
Here is an outline of what the ratings indicate for practical application:
- Less than 5,000 mm/24 hours – lightly water-resistant. I personally find it somewhat misleading when someone advertises a waterproof rating this low. This means this fabric will protect you from mist a one-time light splash, but little more.
- 5,000 mm (often written as 5K waterproof) – water-resistant; stands up to light rain and dry snow, under no pressure.
- 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.
- 20,000 mm (20K) – very waterproof; stands up to heavy rain and wet snow under heavy pressure; this is what I really want for storm skiing, and for serious rainwear.
- More than 20,000 mm – super waterproof under very heavy pressure; this is like what garbage bags and rain boots are rated; great for water protection, but at the cost of sacrificing breathability.
In order for high-tech materials to do their dual duty of keeping external water out and letting internal water vapor (aka perspiration) escape from the inside, manufacturers utilize a variety of different technologies. They all basically involve using a membrane with pores large enough to let water vapor molecules out but not large enough to let liquid water seep in.
Unfortunately, there is not an industry standard to test the transfer rate of water vapor (what we refer to as breathability.) And even if there was an industry standard, things would still be tricky because of how temperature and humidity affect water vapor transfer rate.
Breathability is often reported in terms of the amount of water vapor, in grams, that can pass through a square meter of the material in question during a 24-hour time period (g/m2).
If we momentarily assume that all tests measure moisture vapor transfer rate exactly the same, and that weather conditions don’t change this performance, only then could you fully trust this general breakdown of breathability ratings across the board:
- 5,000 g/m2 or less – slightly breathable; not much perspiration can get through this material.
- 10,000 g/mm2 – breathable enough for moderate activity.
- 20,000 g/mm2 – breathable enough for highly aerobic activity; it lets lots of water vapor out so you don’t get disgustingly sticky when you’re working up a sweat.
In the United States, windproof ratings are often measured in the amount of cubic feet per minute (CFM) of about a 30-mile-per-hour wind that can pass through one square foot of the material. Therefore, a lower number represents more effective wind blocking.
Here’s an outline for the practical application of these numbers:
- 60 CMF – about what an average fleece material is rated; the wind will go right through this.
- 20 CFM – wind-resistant.
- 10 to 5 CFM – very wind-resistant; what most softshells are rated.
- 1 CFM or less – considered windproof.
- 0 CFM – completely windproof; no wind at all will get through and therefore you will experience no convective heat loss.
UPF, Built-In Sun Protection
Sun protection clothing is measured as an Ultraviolet Protection Factor (UPF), which is similar to sunscreens’ SPF (Sun Protection Factor) ratings. The ultraviolet (UV) rays are the part of sunshine that can cause sunburn, premature aging, and skin cancer.
UPF is the fraction of the sun’s ultraviolet rays that can get through the fabric. Here are some numbers to help clarify:
- UPF 5 to 15 – okay to good UV protection, allows between 1/5th or 20%, and 1/15th or 6% of UV rays to get through; this is what most normal clothing provides, which can be enough protection for some skin types and/or for some geographical locations (further from the equator, at lower elevation, etc.).
- UPF 25 – very good protection; allows only 1/25th or about 4% of UV rays to pass through.
- UPF 50+ – excellent protection, what you want if you are a fair-skinned human who plans to spend all day in the sun in the tropics; allows only 1/50th or 2%, or less, of UV rays to get through. This is the best UPF rating you will see in technical outdoor clothing.
It is important to note that the performance ratings of a fabric are limited by other factors such as clothing construction and use. For example, if a fabric is super waterproof yet the seams or zippers are unsealed, you can still get leaks through these weak points. Or if the fabric is breathable but you layer it with something else that is not breathable, then your system is not breathable. If the fabric is windproof but there are laser-cut ventilation zones, you’ll still get wind through those areas. If the fabric has a super high-rated UPF, you still risk sun-related skin damage in the areas that the fabric does not cover. This is all common-sense of course.
Hopefully with all this technical information in your knowledge base, you’ll feel better informed to make a decision next time you are faced with outdoor performance apparel choices.
Kendall Fischer, Content Writer
Post was updated on December 1, 2020