Understanding Waterproof Fabrics: The Essentials of Waterproofing, Breathability, and DWR for Outdoor Enthusiasts

Introduction

When you’re planning an outdoor adventure, one of the most critical pieces of gear is your waterproof jacket. Whether you’re hiking in the hills, climbing mountains, or running trails, having a jacket that keeps you dry and comfortable can make all the difference. In this blog post, we’ll delve into the technical aspects of waterproof fabrics, breathability, and durable water repellency (DWR). Understanding these elements will help you choose the right gear for your activities and ensure it performs well in real-world conditions.

Understanding Waterproof Fabrics

What Makes a Fabric Waterproof?

A fabric is considered waterproof if it can withstand a certain amount of water pressure without letting moisture through. This is measured using the hydrostatic head test, which determines how much water pressure a fabric can handle before it starts to leak. The industry standard for waterproofing is a hydrostatic head rating of at least 1,500mm, meaning the fabric can hold a column of water 1,500mm tall without leaking. For outdoor enthusiasts, a higher hydrostatic head rating indicates better performance in prolonged heavy rain.

Hydrostatic Head Ratings Explained

1,500mm: The minimum standard for a fabric to be classified as waterproof. While suitable for light rain and occasional splashes, it may not hold up under prolonged or heavy rain.
5,000mm: Commonly used in ski jackets, this level of waterproofing is adequate for snow and light rain. However, it may not be sufficient for heavy downpours or long-duration exposure.
10,000mm: Suitable for extended periods of heavy rain. This rating is the lowest we use for our waterproof jackets, ensuring they can withstand significant rainfall and high water pressure from activities like kneeling or wearing heavy backpacks.
20,000mm: Offers excellent performance, capable of withstanding all-day rain, heavy packs, and strong winds. Jackets with this rating are highly durable and reliable in harsh conditions.
30,000mm: The highest performance for extreme conditions, ensuring waterproofness even in storm-force winds. Jackets with this rating are designed for serious mountain conditions and prolonged exposure to severe weather.

Functional Aspects of Waterproofing

The hydrostatic head test simulates the pressure exerted by water on the fabric. While a hard rain might generate around 2 psi (equivalent to about 1,400mm hydrostatic head pressure), activities such as kneeling, sitting, or the pressure from a backpack can significantly increase the pressure on the fabric. For instance, kneeling can generate around 18 psi, and sitting can generate about 7 psi in a person weighing around 170 lbs. Thus, waterproof fabrics need to withstand much higher pressures than just rain to ensure they keep the wearer dry in real-world conditions.

Importance of Seams and Construction

Even the most waterproof fabric can fail if the seams are not properly sealed. All seams in waterproof garments must be factory-sealed or taped to prevent water from seeping through the stitch holes. Additionally, features like zippers, hoods, and pockets need to be designed to keep water out. For example, water-resistant zippers and storm flaps can significantly enhance a jacket’s ability to keep you dry. Rain room tests have shown that garment design can be just as crucial as fabric performance. Poorly designed zippers, hoods, or other features can lead to leaks, even if the fabric itself is highly waterproof.

Real-World Implications

In real-world use, the waterproofness of a garment is a combination of the fabric’s hydrostatic head rating and the overall design of the jacket. A jacket with a high hydrostatic head rating but poor seam sealing or zipper design may still let water in. Conversely, a well-designed jacket with a moderate hydrostatic head rating can perform exceptionally well in keeping you dry. Therefore, it’s essential to consider both the fabric’s rating and the jacket’s overall construction when choosing a waterproof garment.

The Importance of Breathability

What Is Breathability and Why Is It Important?

Breathability refers to a fabric’s ability to allow moisture vapor to pass through it, which is crucial in preventing the buildup of sweat inside the garment. When engaging in physical activities, your body generates heat and moisture. If your jacket isn’t breathable enough, this moisture can’t escape, leading to discomfort and potential cooling as the sweat cools and condenses.

Measuring Breathability: Moisture Vapor Transmission Rate (MVTR)

Breathability is typically measured by the Moisture Vapor Transmission Rate (MVTR), which indicates how much moisture vapor can pass through a square meter of fabric over 24 hours. Here are some typical MVTR values and their implications:

5,000 g/m²/24hrs: Suitable for more stationary activities where perspiration levels are lower.
10,000 g/m²/24hrs: Provides good breathability for moderate activities such as walking, gentle biking, and paddle sports.
20,000 g/m²/24hrs: Ideal for high-intensity activities like strenuous hiking, mountaineering, and running, where high breathability is essential to stay comfortable.
30,000 g/m²/24hrs: Exceptional breathability for very high-intensity activities and harsh conditions, ensuring that sweat is efficiently wicked away from the body.

Functional Aspects of Breathability

Breathability in waterproof fabrics is a balancing act. To keep water out while allowing moisture vapor to escape, manufacturers use various technologies, including microporous membranes and hydrophilic coatings. Microporous membranes have tiny pores that are small enough to block liquid water but large enough to allow water vapor to pass through. Hydrophilic coatings, on the other hand, absorb moisture vapor and then move it through the fabric by a process of diffusion.

Real-World Scenarios

In practical terms, breathability prevents the buildup of sweat, which can make the wearer feel clammy and damp. This is particularly important in outdoor activities where comfort and safety are paramount. For example, in cold conditions, trapped sweat can cool rapidly, leading to discomfort and even hypothermia. Thus, choosing a jacket with appropriate breathability for your activity level is crucial.

Breathability Challenges

Breathability is affected by various factors, including external temperature, humidity, and the wearer’s activity level. In cold or humid conditions, the dew point (the temperature at which moisture condenses) can be inside the garment, reducing its ability to breathe effectively. Additionally, dirt and body oils can clog the pores of breathable membranes, diminishing their performance over time. Regular cleaning and maintenance are necessary to ensure that the fabric retains its breathability.

Durable Water Repellency (DWR)

What Is DWR and How Does It Work?

Durable Water Repellency (DWR) is a coating applied to the outer layer of waterproof fabrics. Its primary function is to make water bead up and roll off the surface of the fabric rather than soaking in. This serves as the first line of defense against moisture, helping to prevent the fabric from becoming saturated and maintaining the effectiveness of the waterproof membrane underneath.

How DWR Is Applied

DWR treatments are usually applied to the face fabric of waterproof/breathable fabrics during the manufacturing process. There are different methods of application, including spraying, dipping, or adding to a washing cycle. Some treatments are applied before the fabric is laminated with a waterproof membrane, while others are applied afterward.

Degradation and Reapplication

Over time, the DWR coating can wear off due to exposure to dirt, oils, and regular wear and tear. You can tell when the DWR is no longer effective if water stops beading on the fabric and instead starts to soak in. This is known as “wetting out,” which can lead to the fabric feeling damp and reducing its breathability.

To maintain the effectiveness of the DWR coating, it’s essential to reapply it periodically. This can be done using aftermarket DWR treatments, which come in both spray-on and wash-in forms. Brands like Granger’s, Nikwax, and ReviveX offer products specifically designed for this purpose.

Environmental Considerations

Traditional DWR treatments often contain fluorocarbons (PFCs), which have been found to persist in the environment and have harmful effects. Many manufacturers are now moving toward PFC-free DWR treatments, which are more environmentally friendly but may require more frequent reapplication and care.

Common Misconceptions About Waterproof Ratings

Higher Waterproof Ratings Are Not Always Better

A common misconception is that higher hydrostatic head ratings automatically mean better waterproof performance. While higher ratings do indicate a greater ability to withstand water pressure, they can also come at the expense of breathability. For example, a jacket with an extremely high waterproof rating might be less breathable, making it uncomfortable for high-intensity activities where sweat and moisture buildup need to escape.

The Role of Garment Design

Waterproof performance is not solely dependent on the fabric’s hydrostatic head rating. The overall design of the garment, including seam sealing, zipper construction, and hood design, plays a crucial role. Even a fabric with a high waterproof rating can fail to keep you dry if the seams are not properly sealed or if water can enter through poorly designed zippers or hoods.

Real-World Performance vs. Lab Tests

Lab tests for waterproof ratings often do not account for real-world conditions. For example, the pressure exerted on a jacket when kneeling or carrying a heavy backpack can be much higher than the pressure exerted by rain alone. Therefore, it’s important to consider how the jacket will perform in your specific activities and conditions rather than relying solely on lab test ratings.

Caring for Your Waterproof Fabrics

Importance of Regular Maintenance

To ensure your waterproof garments continue to perform well, regular maintenance is essential. Dirt, sweat, and oils can clog the pores of breathable membranes and degrade the DWR coating, reducing the effectiveness of your jacket. Regular cleaning according to the manufacturer’s instructions will help maintain the fabric’s performance.

Steps for Washing and Reproofing

Cleaning: Use a gentle detergent specifically designed for technical fabrics. Regular detergents can leave residues that clog the fabric’s pores. Avoid fabric softeners and bleach, which can damage the waterproof membrane.
Drying: After washing, air dry your garment or tumble dry on a low setting. Heat can help reactivate some types of DWR coatings.
Reapplying DWR: Once clean, apply a DWR treatment according to the product’s instructions. For spray-on treatments, apply evenly to the outside of the garment. For wash-in treatments, add to the washing machine during the rinse cycle.
Heat Activation: Some DWR treatments require heat activation. Use a tumble dryer on a low setting or iron the garment (if the care label allows) to help set the DWR coating.

Extending the Lifespan of Your Waterproof Gear

Proper care can significantly extend the lifespan of your waterproof gear. Store your garments in a cool, dry place away from direct sunlight. Avoid compressing them for long periods, as this can damage the waterproof membrane and DWR coating. By following these maintenance tips, you can ensure your gear remains effective and comfortable for many adventures to come.

Conclusion

Choosing the right waterproof jacket involves understanding the balance between waterproofness, breathability, and DWR. By considering the hydrostatic head rating, breathability, and the role of DWR, you can select a jacket that suits your specific needs and activities. Remember, the best jacket is one that is well-maintained and cared for, ensuring it performs well when you need it most.

Whether you’re tackling a mountain summit, enduring a rainy hike, or running trails in unpredictable weather, having the right gear can make all the difference. Invest in quality waterproof clothing, maintain it properly, and enjoy your outdoor adventures with confidence.