Water­density Membrane

THE FILM THAT DOESN'T LET WATER THROUGH

Functional jackets offer protection from the wet, offering both waterproof and breathable properties. They keep you dry in the rain but allow water vapor generated by your body heat and activity to escape. Functional jackets achieve these properties through their special fabrics, sealed seams, and water-repellent finishes.
The waterproof, breathable fabrics of a functional jacket are called laminates because they consist of several interconnected layers of fabric. This is why you'll often hear about two- or three-layer jackets in specialty stores. In the most common form, a laminate consists of three layers: outer fabric, membrane, and inner fabric.
Membranes are ultra-thin separation layers that prevent water molecules from entering the jacket while still allowing water vapor to escape. Various technologies can be used for this purpose. Today, so-called microporous membranes are most commonly found in the outdoor industry.

Microporous membranes
Microporous membranes have many small pores in the carrier material. The pores are designed to be smaller than a water molecule but larger than a vapor molecule. This achieves the desired waterproofness while maintaining breathability. Microporous membranes are widely known and widely marketed today under the brand name GORE-TEX®. The plastic polytetrafluoroethylene, or PTFE for short, serves as the base material for microporous GORE-TEX® membranes. PTFE is often referred to colloquially by the trade name "Teflon," as the plastic is primarily known in everyday life from non-stick frying pans. PTFE is extremely durable, very inert, and almost no materials stick to PTFE. The PTFE achieves its micropores by deliberately stretching the material. After the stretching process, it is referred to as expanded polytetrafluoroethylene – or ePTFE for short. Microporous ePTFE membranes function in all conditions, are highly breathable, and extremely robust. However, the functional advantages of the material are offset by significant ecological and toxicological disadvantages.

Problematic production and disposal
On the one hand, the production of ePTFE requires large amounts of energy and toxic chemicals – ePTFE belongs to the PFAS group of substances. PFAS are practically impossible to degrade through natural processes. Therefore, if they enter the environment, they persist for a very long time – and their concentrations are continuously increasing. PFAS can now be detected practically everywhere in Europe, including in drinking water. Some PFAS are also known to cause serious health problems in humans.
You can find answers to the most important questions about PFAS in this blog post (link to ROATUF knowledge: PFAS in the outdoor industry).

On the other hand, the disposal of ePTFE is extremely difficult, as polytetrafluoroethylene can only be disposed of by incineration. This produces highly toxic hydrofluoric acid, which must be neutralized in incineration plants. Many rain jackets, however, do not end up in our high-tech waste incineration plants; because of their robustness and the emotional attachment of the former wearer, many owners, with the best of intentions, donate their "hardshells" as used clothing. This is how they end up in countries without regulated waste disposal. If they end up in a landfill there, the ePTFE membranes do not degrade. If they are eventually burned in an open fire, the toxic substances are released directly into the environment or are inhaled. Inhaling hydrofluoric acid vapors burns the lungs, leads to the formation of pulmonary edema, and is fatal within a short time, even at low concentrations.

Hydrophilic membrane
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, but instead wick water vapor away to the outside using a physical-chemical principle. Hydrophilic molecular chains in the membrane absorb sweat and transport it to the outside. 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 the outside and inside of the jacket are roughly the same temperature and humidity, moisture transport is limited. In extreme cases, where the humidity and heat outside the jacket are higher than inside, the moisture can even be transported in the wrong direction. For example, during a summer thunderstorm or in a tropical rainforest. Hydrophilic membranes are also typically somewhat less vapor-permeable and more robust than microporous ePTFE membranes.

Environmentally friendly production
These functional differences between microporous and hydrophilic membranes are irrelevant for the average to ambitious outdoor athlete. Both technologies offer proven, reliable, and long-lasting protection against the elements. However, unlike microporous ePTFE membranes, hydrophilic membranes can be manufactured in an environmentally friendly and recyclable manner. ROTAUF uses Sympatex® laminates in its products. The German company is fully committed to the sustainability of its products and produces polyester-based membranes. These require significantly less energy to manufacture and are completely free of PFAS and other toxic chemicals. Sympatex® membranes have the additional advantage that all three fabric layers of the laminate can be made from the same material, which increases recyclability. Sympatex® is working with partners to close the textile cycle for functional clothing nationwide by 2030 and achieve 100% circular production.

In practice, the waterproofing of a fabric is at least as important for the high level of climate comfort of an outdoor jacket as the membrane. The protective layer on the outer fabric, known in technical jargon as DWR (Durable Water Repellency), ensures that raindrops roll off, thus preventing the fabric from absorbing water.