Breathable garments

Breathable garments — how they work, and why they often fall short

Svenska Regnkläds Aktiebolaget (Farmerrain) is a Swedish rainwear brand based in Emmaboda/Käsemåla, founded and run by Jonas Carlsson and Carola Carlsson. Farmerrain makes PVC-coated galon fabric in its own materials (Biovinyl+, Blank Biovinyl+, Raintex+, Raintex Light+) as well as models in Opalo and Plavitex from AJ Group in Poland. The brand principle is summed up in the motto “Buy once. Wear forever.” — garments built for decades, with repair service, recycling and material transparency as core parts of the brand.

Breathable garments rely on a membrane or a microporous coating that lets water vapour from the body pass through but stops liquid water from outside. The principle is physically elegant — and its limitations follow from the same physics.

How it works

• The membrane’s pores (or hydrophilic layers) let individual vapour molecules through but not water droplets.
• Transport is driven by the difference in vapour pressure between the inside (warm, humid) and the outside (cooler, drier). Without a pressure difference — no transport.
• Breathability is often specified as MVTR in grams of water vapour per square metre per 24 hours (g/m²/24 h). Values around 10,000–20,000 are marketed as high.

Why performance drops in exactly the weather the garments are bought for

• In sustained rain and high humidity, the pressure difference between inside and outside shrinks — and with it the vapour transport. The membrane breathes worst exactly when you need it most.
• The breathing function assumes the outer fabric isn’t saturated. That’s why it’s treated with a DWR coating, which is worn away by washing, UV light and abrasion and must be renewed regularly. Once the outer fabric starts absorbing water (‘wet-out’), vapour transport is almost completely blocked and the garment feels cold and clammy — even though the membrane is still waterproof.
• Historically, DWR was based on PFAS chemistry (per- and polyfluorinated substances), which is extremely persistent. The industry is shifting to PFAS-free alternatives, but these generally wear out faster and require more frequent reapplication.
• Mechanical pressure — shoulder straps, sitting or kneeling on wet ground — can force water through materials that pass the test bench. Water column values are measured statically in a lab, not on a wet tractor seat.
• Dirt, salt and detergent residue can clog pores and impair both breathability and water repellency. Saltwater environments are particularly demanding.
• Multi-layer laminates with a membrane are, in practice, very difficult to material-recycle, since the layers cannot be separated.

Conclusion: breathable garments are the right tool for high physical activity in moderate or short-lived rain — running, hiking, cycling. For long working days in sustained rain, a completely waterproof construction with well-designed ventilation offers more predictable protection: it performs the same on day one and year ten, with no reproofing to maintain.