Rain gear: waterproof, breathable, reproofed

A rain jacket usually consists of several layers: a face fabric outside, a waterproof layer – a membrane or a coating – and often a lining or protective layer inside. The waterproof layer stops liquid water but lets water vapour through. For that to work, it has to be warmer and more humid inside than outside. The vapour then moves from the “full” area to the “empty” one, roughly the way a smell spreads through a room.

The smaller that difference, the less vapour escapes. On a cold, dry day a breathable jacket therefore works well. On a warm, muggy rainy day, when there is almost as much moisture in the air outside as inside, only a little vapour gets out.

The face fabric has a water-repellent finish, often called DWR (durable water repellent). It makes rain bead up. When it wears off, the face fabric soaks up water. Then a film of water forms on the outside that slows the vapour further. The jacket is usually still waterproof, but it feels cold and clammy inside.

No material stays completely dry inside during hard exertion. When you work hard or walk uphill fast, you produce more sweat than any membrane can release. In the cold, the vapour can also condense on the inside of the jacket, much like condensation on a window. Many people take this for a leak, even though the jacket is waterproof.

There are real leaks too, of course: at seams whose sealing tape has come loose, at cuffs where water runs in, or at a hood that does not close well. Water can also wick upwards through clothing from below if the jacket is too short or your trousers get wet.

Good to know: a poncho or an umbrella lets plenty of air circulate and is often more pleasant than a closed jacket on paths in warm rain. In wind, though, both are unsuitable.

When buying, the details count more than lab values: a hood with a peak that can be adjusted and turns with your head (and fits over a helmet if needed); vent zips under the arms or at the sides; taped seams; a length that reaches below the hips; cuffs that can be closed. Think about what you need the jacket for: short showers in daily life, long rainy days in the mountains or wind on the coast make different demands.

On the way, you decide a lot about the result yourself. Adjust your pace, open zips before you are soaked with sweat and do not wear more under the jacket than necessary. Layers underneath that are too warm almost always lead to sweat. At breaks you then put a warm layer under or over the jacket.

In the layering system, the rain jacket is the outermost protective layer. It works together with the base and mid layers. Rain trousers complete it in long rain and wind.

Many people never wash their rain jacket for fear of damaging the membrane. Often the opposite is right: dirt, sunscreen and skin oils weaken the water-repellent finish and can reduce breathability. So wash the jacket when it is dirty, exactly as the manufacturer instructs and with a suitable detergent.

Fabric softener is off-limits: it can leave deposits on the fabric and membrane and weaken the finish. Some manufacturers also mention heat, for example in a tumble dryer, as a way to reactivate the water repellency – but only if the care label allows it.

If water no longer beads up after washing but soaks into the face fabric, it is time to reproof. There are wash-in and spray-on products for this. Use them according to the manufacturer's instructions, and use sprays only outdoors or with good ventilation. The manufacturer's care instructions always take precedence.

Wetness from outside or sweat from inside makes clothing insulate less well. Add wind and cold, and the risk of hypothermia rises – even in summer in the mountains. Watch for feeling cold, intense shivering, clumsy hands or confusion. Put on dry layers in time, find shelter from wind and rain and with serious signs get help via the local emergency number (112 in the EU).

In rain you see less well and are seen less well. Bright or conspicuous colours help you be noticed on roads or in open country. A hood also limits hearing and side vision – look around deliberately when crossing roads.