JARGON BUSTER
How waterproof?
Water-resistant, water-repellent, weatherproof and waterproof. They sound like they mean the same thing, but actually they’re all quite different. A water-resistant fabric has tightly woven fibres that naturally resist penetration by moisture. It might stand up to light drizzle but not heavy rain. A water-repellent fabric has a finish to further enhance its ability to shed water. This might be a wax coating or a durable water repellent (DWR) treatment. Then there are weatherproof fabrics, which aren’t strictly waterproof under laboratory conditions, although they provide decent protection out there in the real world. But a waterproof fabric is lab tested as being impervious to water, even under pressure (up to a point, since there are degrees of waterproofness – see hydrostatic head later on in this guide).
Breathability
As well as the level of water-resistance on offer, breathability is the other critical performance element of a waterproof fabric. Put simply, it’s what enables moisture from inside your jacket to escape, stopping you from becoming a stuffy, clammy mess. It’s a misleading term, because it implies that it has something to do with breathing or air, but actually, in garment terms, breathability simply refers to a material’s ability to move moisture. Remember that it’s still about keeping you dry, not about ventilation or keeping you cool. A breathable jacket doesn’t stop you from getting hot and sweaty, but it should gradually move moisture vapour away to keep you more or less dry and comfortable.
Waterproof membrane
The basis of all hard shell jackets, a membrane is a thin layer that is impenetrable to liquid water but allows moisture vapour to move through it (hence waterproof-breathable, or WP/B). Membranes are usually made of ePTFE (expanded polytetrafluoroethylene) or PU (polyurethane). They are generally laminated to the inside of the face fabric of a jacket and are therefore sometimes referred to as ‘laminates’.
Face fabric
This refers to the outer layer of a waterproof jacket, which is usually made from polyester or nylon. The face fabric protects the membrane from abrasion and dirt, and aids water repellency by providing a surface on which to apply a DWR.
DWR treatment
AKA a Durable Water Repellent treatment, this finish is largely what causes rain to bead up and roll off your jacket. It’s an essential part of modern waterproofs, because if the face fabric becomes saturated (a process called ‘wetting out’) the membrane cannot breathe effectively, leading to moisture build-up inside your jacket. Unfortunately, Durable Water Repellent treatments are not actually very durable – in fact, they can degrade quite quickly. This is why regularly cleaning and reproofing your waterproofs with specialist products is so important.
Backer or liner?
A backer is used on the inner surface of waterproof-breathable fabrics to protect the membrane and provide extra comfort. A 2-layer jacket has no backer, instead employing a separate mesh or taffeta drop liner. A 2.5-layer jacket uses a raised print or pattern (considered a ‘half-layer’, hence 2.5), while a 3-layer jacket uses a full bonded textured or mesh layer that creates a sort of sandwich, with the membrane in the middle and the face fabric on the outside. 3-layer jackets make for the most durable and effective shells but are also the most expensive. 2.5-layer jackets are cheaper, lighter and more packable, but can sometimes feel a little clammy. 2-layer jackets are comfortable to wear, but the need for a separate liner makes them bulkier and heavier.