Functional clothing for fall and winter is part of a huge market. Last year alone, Germans spent seven billion euros in sports stores – and the trend is rising.
The solution for athletes comes from chemistry labs. Fibers made of polyester or polypropylene, the stuff plastic bags are made of, are almost perfect for sports underwear. The shirts and briefs are sold in sports stores as “functional underwear.” They attract sweat without retaining it, allowing the small drops to evaporate on the surface. When the weather gets bad, it’s not enough for sportswear to merely wick away sweat. It must also protect against wind and rain.
In 1875, the Norwegian captain Helly Hansen observed how his sailors painted their cotton clothing with oil paint to protect themselves from wind and weather – and had an idea. The clever sailor invented the first oilskin, the Ostfriesennerz. A good start. Modern sportswear performs a balancing act, so to speak. It protects the body from rain and storms. It wicks sweat drawn from the underwear to the outside, is lightweight and flexible.
Many jackets manage this with membranes – thin films that are welded or glued between the layers of fabric in the jacket. Under the microscope, these layers look like a torn yeast dough. On one square centimeter, a membrane has 1.4 billion pores. Our body heat pushes water vapor – that is, sweat – from the inside to the outside. The pores of the membrane are large enough to allow water vapor molecules to pass through on their way out. A drop of water, on the other hand, is 20,000 times larger than a pore in the membrane – and therefore rolls off the surface.
Advertising agencies have come up with a fancy vocabulary for the property of membranes to allow water vapor to escape from the inside to the outside: breathable. “A pure marketing buzzword,” says Thomas Meyer zur Capellen. In fact, breathable only stands for water vapor permeability.
There are two main types of membranes. Variant one is windproof. These fabrics are thinner than their waterproof counterparts and allow more vapor to pass through. Normally, they keep the body dry, but moisture will eventually come through the seams during a thundershower. Variant two are waterproof membranes. They feel stiffer, but can withstand a one-hour steady rain during a walking tour. A third type of functional clothing does without a membrane: Jackets made of microfiber. Ten kilometers of microfiber yarn weigh just one gram, and there are models that weigh only 85 grams. When crumpled up, they fit into the breast pocket of an outer shirt. And because the jacket is very tightly woven, water rolls off and wind doesn’t get through. Only in prolonged rain does even the microfiber allow moisture to penetrate inside.
All these jackets have one thing in common. They keep out wind and water – but they don’t keep you warm. That’s because they have no lining. That’s why runners, cyclists and walkers need another layer of clothing between their underwear and jacket. A sweatshirt? Such a cotton sweater has the same properties as cotton underwear: If the fabric is wet, it sticks to the body and no longer keeps warm. Fleece works better. Like functional underwear, fleece (English for “fluff”) is often made of polyester and is permeable to water vapor.
The latest trend in sportswear is the softshell sports jacket. These sports jackets already have the fleece sewn in for cold days, and their surface is soft, in other words. Softshells are suitable for 90 percent of all outdoor activities, for an athlete who jogs for an hour, for hikers, cyclists, inline skaters.
