What is Waterproof Breathable Fabrics?

Innovative Comfort: The Science Behind Waterproof and Breathable Fabrics

Waterproof breathable fabrics are specialized textiles designed to keep you dry while allowing moisture to escape during physical activity. These fabrics, typically constructed with two or three layers, are widely used in outdoor clothing such as waders, rain jackets, ski and snowboard gear, hiking apparel, and various industrial applications. Their functionality relies on a key principle: the fabric’s pores are too small for water droplets to penetrate but large enough to allow body vapor to escape. This is achieved through either laminate technology or coatings.
These fabrics are classified into two main types based on their structural composition:

1. Microporous Coatings or Films:
   Featuring hydrophobic, laminated, or coated structures, these fabrics have microscopic pores that allow water vapor to escape while blocking liquid water.
2. Hydrophilic Coatings or Films:
   Nonporous by nature, these coatings absorb water vapor on one side and prevent liquid water from passing through.

Some fabrics combine elements from these categories to enhance performance.

To maintain their effectiveness, waterproof breathable fabrics are often treated with Durable Water Repellent (DWR) coatings. DWR causes water to bead up and roll off, preventing the outer layer from becoming saturated and helping sweat vapor escape more efficiently. However, DWR treatments degrade over time due to exposure to dirt, oils, and washing. Regular cleaning and reapplication of DWR are necessary to sustain performance.

The functionality of these fabrics also depends on relative humidity. When the interior is more humid than the exterior, moisture moves outward, and vice versa. DWR treatment ensures the outer surface remains dry, facilitating moisture escape. The outermost fabric layer, known as the face fabric, plays a critical role in this process, as it directly impacts breathability and moisture management.

Microporous Coatings and Membranes
Microporous coatings or membranes feature tiny pores that permit vapor to pass while blocking larger raindrops, thus providing breathability and water resistance. These are constructed from polymers (such as PU) with hydrophobic properties that deter water. To create a spongy or foamy texture, chemical blowing agents are introduced to the coating material, releasing gas and solidifying into a microporous coating. These coatings have approximately 1.2–1.4 billion minuscule holes per square centimeter, with pore sizes between 0.1 and 1.0 micrometers—smaller than raindrops but larger than vapor molecules. This structure forms a barrier that stops external moisture, such as rain or snow, from entering, while enabling internal moisture like sweat vapor to exit. The water-repellent nature of these coatings or membranes causes water droplets to form beads on the fabric’s surface and roll off.

Hydrophilic Coatings and Membranes
Hydrophilic membranes or coatings are solid, nonporous substances that facilitate moisture movement through a distinctive process. They employ hydrophilic functional groups within molecular chains to transport moisture vapor via diffusion. The membrane or coating absorbs moisture on one side, transports it through the film or coating, and discharges it on the opposite side. This results in a three-step process: the coating extracts sweat from the skin, the middle layer disperses it, and the outer layer expels it for evaporation.

Waterproofness and Breathability Ratings
Waterproof breathable materials serve two primary functions: protecting against water and allowing air to pass through. Waterproofness is the material’s ability to block water from seeping in, while breathability refers to its ability to let water vapor escape. Since it’s not possible for a fabric to be entirely both waterproof and breathable at once, waterproof breathable fabrics strike a balance between these two properties, offering a compromise between protection from water and the ability to release moisture. The ideal choice depends on your specific use. By considering the waterproof and breathability ratings of outdoor gear, you can select the right option for your preferred activities and environmental conditions.

Waterproofness
Waterproofing is measured by hydrostatic pressure, which indicates the amount of water pressure the fabric can withstand over 24 hours, typically expressed in millimeters (mm). A rating of 20,000 mm/24hr is considered the benchmark for complete waterproofness.

Breathability
The permeability of a fabric is measured by the rate at which water vapor can escape, expressed in grams of moisture that pass through a square meter of fabric over a 24-hour perod. The higher the moisture vapor permeable (MVP) rating, the more breathable the fabric is.

After learning about waterproof breathable fabrics, you may want to experience the balance between waterproofing and breathability. Most outdoor products on the market use either coatings or laminates, both of which provide similar waterproof and moisture-permeable functions, but with varying levels of performance.

Waterproof breathable fabrics are versatile and essential materials with numerous practical applications in daily life. Whether you’re an avid outdoor sports enthusiast or simply looking to stay dry in wet weather, there’s a waterproof breathable fabric designed to meet your needs. By understanding the different types of waterproof breathable fabrics and their mechanisms, you can make informed choices when selecting clothing that offers reliable protection from the elements.

Waterproof Breathable Fabric Care
Proper care is essential to maintain the performance of technical outerwear after outdoor activties. To clean most waterproof breathable clothing, follow these tips:

1. Use a low-speed setting on your washing machine instead of dry cleaning.
2. Choose a neutral laundry detergent and avoid fabric softeners, bleach, or stain removers.
3. Tumble dry on low heat to refresh the DWR (Durable Water Repellent) coating, but always follow the care label to avoid damage from high temperatures or ironing.
4. Secure all zippers and closures, loosen any elastics, and consider using a mesh laundry bag to protect your gear.