Being prepared for any situation is something most people desire. You feel safe when nothing unexpected can happen. However, perhaps fortunately, we often carry our "superhero suit" around unnecessarily. Of course, our shoes are also part of our superhero equipment. Before we head out in the morning, we look out the window, choose the right shoes, and feel safe, perfectly prepared for the day. We glance down, our chin touches our chest, and we see it’s the same pair as yesterday, the same as the days before. It might spontaneously start raining, and we want to be prepared. Wet feet—none of us wants that.

Footwear developers can help in various ways. Be it with water-repellent textiles, good old leather, or high-tech membranes, designing a shoe to protect against water is no longer a major challenge.

Using membranes is always an excellent solution. Manufacturers offer a wide variety of options. There’s the classic microporous membrane, which resists the surface tension of individual water drops but allows moisture excreted by the foot to escape. Or there are hydrophilic membranes that absorb moisture in the yarn's middle and can transport it outside if the climate inside the shoe differs from that outside. These are great membranes typically used as a bootie construction. Several different layers around the membrane make the bootie durable and serve as a lining toward the foot. Another solution is laminating the membrane to the upper material, which requires creating the lining separately. This also has advantages, as it allows for different types of lining materials. Here, the upper material doesn’t have to be pre-treated with DWR. Many people don’t realize that standard membranes provide double protection against water. Membrane manufacturers require DWR-treated materials for the upper so that rainwater cannot collect between the upper and the membrane bootie.

DWR—Durable Water Repellent—is self-explanatory. Textiles and leather undergo a chemical treatment. Unfortunately, most of these treatments involve permanent chemicals called PFAS (Per- and Polyfluoroalkyl Substances). PFAS are water and dirt repellent but are highly harmful to the environment and health. There is probably no place or living being on earth that is not already contaminated by PFAS. This poses a significant challenge for material suppliers and manufacturers to develop treatments that do not harm us or the environment. Solutions may involve changing the surface structure of fabrics or using natural-based oils and waxes. Some brands have managed to become PFAS-free, but the majority still face the quality difference between "green" and PFAS-treated materials.

Is leather the sustainable solution? Leather is generally considered to have very positive properties. The raw material is available as long as humans use animals for food. However, there are significant differences, starting with the tanning process and the finishing chemicals. Naturally tanned leather treated with oils or waxes and properly cared for is an excellent solution for daily use. But leather, as a natural product, probably needs more care and attention than technical textiles. Leathers with a DWR finish are 100% waterproof, as are those coated with a type of PU finish. Additionally, any textile with a coating, from PU to bio-based, is generally waterproof.

As you can see, we developers have various options for making a shoe waterproof. Using a membrane is certainly the most commercial and safest solution. Without a membrane, attention must be paid to seams that perforate the material. Here it is crucial to use perfectly placed lines and select waterproof yarns for the seams. A rubber rand, especially on hiking boots, not only has a mechanical protective function but can also allow crossing water without getting wet.

Interestingly, for certain uses or sports, we deliberately avoid waterproof shoes. In running or trail running, we accept wet feet and dry our shoes after the activity.

I hope we can phase out PFAS as soon as possible and that developers will finally be offered functional, environmentally and human-friendly treatments for our footwear materials from all fabric suppliers. None of us wants to use these harmful substances anymore. Whether to use a membrane or not is certainly a matter of taste—it's up to the customer to decide. This decision likely depends on the desired breathability; sometimes, you build up more unwanted moisture inside the shoe than what comes from outside.

Let’s try again to take off the superhero costume sometimes and dance or jump home barefoot through the summer rain. Just like we all did as children: knocking at the front door, completely soaked, greeting our mom with a smile on our face, full of happiness.

Autor: Martin Waibel