The Function and Sustainability of Waterproof Membranes

ROTAUF - Wasserdichte Membranen

Function and Sustainability of Waterproof Membranes

As an outdoor enthusiast, you enjoy being outside and active. For this, you need good weather protection. Functional jackets, which are both waterproof and breathable, provide this for you. They keep you dry in the rain while allowing moisture vapor from your body to escape. Functional jackets achieve these properties through their special fabrics, sealed seams, and water-repellent coatings.

The waterproof, breathable fabrics of a functional jacket are called laminates because they consist of several interconnected layers of fabric. That's why in specialty stores, you often hear about 2- or 3-layer jackets. In the most common form, a laminate consists of three layers: outer fabric, membrane, and inner fabric.

Membranes are ultra-thin barrier layers that prevent water molecules from entering the jacket while allowing water vapor to escape. Various technologies can be used for this purpose. The most common in the outdoor industry today are so-called microporous membranes.

Microporous Membranes

As the name suggests, microporous membranes have many small pores in the carrier material. These pores are designed to be smaller than a water molecule but larger than a vapor molecule, achieving the desired waterproofness while maintaining breathability.

Microporous membranes, widely known today under the brand name GORE-TEX®, are typically made from the plastic polytetrafluoroethylene, abbreviated as PTFE. PTFE is commonly referred to colloquially as "Teflon" because it is mostly known from non-stick frying pans in everyday life. PTFE is extremely durable, chemically inert, and there are virtually no materials that adhere to it.

The micropores in PTFE are created through a process of stretching the material. After the stretching process, it is referred to as expanded polytetrafluoroethylene, or ePTFE. Microporous ePTFE membranes perform well in all conditions, offering high breathability and durability. However, the functional advantages of the material are accompanied by significant ecological and toxicological drawbacks.

Problematic Production and Disposal

On the one hand, the production of ePTFE requires large amounts of energy and toxic chemicals. ePTFE belongs to the group of substances known as PFAS. PFAS are practically non-biodegradable by natural processes. Once they enter the environment, they persist for a very long time, continuously accumulating. PFAS can now be found virtually everywhere in Europe, including in drinking water. Some PFAS are also known to cause serious health problems in humans. Answers to the most important questions about PFAS can be found in this blog post (Link).

On the other hand, the disposal of ePTFE is extremely challenging. Polytetrafluoroethylene can only be incinerated for disposal. This process produces highly toxic hydrofluoric acid, which must be neutralized in the incineration plants. However, many rain jackets do not end up in high-tech incineration plants. Due to their durability and emotional attachment, many owners donate their "hardshells" with the best intentions as second-hand clothes. Consequently, they end up in countries without regulated waste disposal systems. If they end up in a landfill there, the ePTFE membranes do not decompose. If they are eventually burned in open fires, the toxic substances are released directly into the environment or inhaled. Inhaling hydrofluoric acid vapors corrodes the lungs, leading to the formation of pulmonary edema and can be deadly even at low concentrations in a short period.

Hydrophilic Membranes

For these reasons, ROTAUF completely avoids the use of ePTFE membranes. Instead, we use so-called hydrophilic membranes in our waterproof jackets. These membranes do not have pores like microporous membranes; instead, they transport moisture outward through a physical-chemical process. Water-attracting molecule chains in the membrane absorb sweat and transport it outward. At the same time, the hydrophilic membrane prevents water and wind from penetrating from the outside.

To function optimally, hydrophilic membranes require a certain temperature and humidity difference between the inside and outside of the jacket. If it is approximately the same temperature and humidity inside and outside the jacket, moisture transport is only limited. In extreme cases, where humidity and warmth outside the jacket are higher than inside, moisture can even be transported in the wrong direction, such as during a summer storm or in the tropical rainforest. Hydrophilic membranes are typically slightly less breathable and robust than microporous ePTFE membranes.

Environmentally Friendly Production

For the average to ambitious outdoor enthusiast, these functional differences between microporous and hydrophilic membranes are not relevant. Both technologies offer a proven, reliable, and durable protection against the elements. However, unlike microporous ePTFE membranes, hydrophilic membranes can be produced in an environmentally friendly and recyclable manner.

ROTAUF uses Sympatex® laminates in its products. The German company is dedicated to the sustainability of its products and produces membranes based on polyester. These require much less energy for production and completely avoid PFAS and other toxic chemicals. The Sympatex® membranes have the additional advantage that all three layers of the laminate can be made from the same material, increasing recyclability. Sympatex® is working with partners to close the textile cycle for functional clothing by 2030 and to produce 100% circularly.

In practice, the impregnation of a fabric for high climate comfort of an outdoor jacket is at least as important as the membrane. The so-called DWR (Durable Water Repellency) treatment on the outer fabric ensures that raindrops bead off and prevents the fabric from becoming saturated with water. There are also significant differences in environmental terms with DWR treatments. We'll explore these in the next blog post.

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