What Is a Waterproof Membrane?

A waterproof jacket is an assembly. Confusing one part of it with the whole is the source of most of the misunderstanding in the category, including the belief that a soaked outer fabric means a failed jacket.

The face fabric is the outer textile: it takes abrasion, carries the repellent finish and determines much of the jacket's hand and weight. The membrane or coating is the barrier that stops liquid water. A backer or lining protects the barrier's inner face. The DWR finish makes the face fabric shed water so it does not saturate. Seam sealing closes the needle holes made when panels are sewn together. A laminate is the bonded stack of these fabric layers, not a separate performance property.

Rab draws the line between the two types of barrier explicitly: a coating is a liquid applied to the fabric to form a flexible, durable barrier, while a laminate is a fine membrane made separately as a sheet and then bonded to the face fabric. Coated garments are not automatically inferior — but the two are made differently, and the word membrane properly describes only the second.

Microporous membranes contain a structure of holes far smaller than a water droplet but large enough for individual vapour molecules. Non-porous or hydrophilic membranes have no pores: moisture is absorbed on the humid side, diffuses through the polymer and evaporates on the dry side. Sympatex publishes the clearest description of the second type — a non-porous membrane of billions of hydrophilic molecules, moving moisture by a physio-chemical process.

Pertex documents both approaches under one brand name: a solid non-porous membrane whose moisture transport is molecular diffusion, and a hydrophobic microporous membrane with holes far smaller than a water droplet. So the platform name alone does not tell you which mechanism a particular garment uses.

A third, rarer category is deliberately air permeable. Pertex describes Shield Air as an electrospun nanofibre web with an open network of interconnected pores, and Polartec publishes an air-permeability figure of about 2 l/m²/s for NeoShell to ISO 9237. Most waterproof membranes are effectively airtight, which is what makes them windproof.

Disclosure varies enormously, and it is worth knowing which is which before comparing platforms.

Fully published: Sympatex names the polymer family and the non-porous mechanism. Pertex names both mechanisms and the electrospun structure of Shield Air. eVent's membranes are named as expanded PTFE with millions of pores in a corporate release.

Partly published: Gore names its newer membrane as expanded polyethylene and describes it as PFC-free, without characterising the pore structure on that page. The North Face names a nanospun polyurethane fibre structure for FUTURELIGHT and a nanospinning process, without classifying it as microporous or non-porous. Helly Hansen describes HELLY TECH as an in-house system using a microporous membrane, without naming the polymer.

Not published: Columbia's own Omni-Tech material describes a multilayer construction without saying whether the barrier is a membrane or a coating — notable because Columbia does call OutDry Extreme a membrane. Patagonia's H2No is a performance standard applied to laminates from more than one source, so there is no single structure to publish. We record both as not publicly specified rather than assigning them a category.

Four different roles hide behind the logos on a hangtag, and separating them explains a lot of apparent contradictions.

A membrane manufacturer makes the barrier itself — Gore, Sympatex and eVent are examples that publish the polymer they make. A technology platform is a licensed name and specification which may include garment-level certification: Gore's requirement that finished garments be built and seam-taped to its specification is why construction is comparatively consistent across the brands using it. A brand-owned platform such as HELLY TECH is described by the brand as its own system. And a performance standard such as H2No is a testing regime applied to fabrics from multiple suppliers, so two garments carrying the name need not share a membrane.

The practical consequence: a platform name tells you which specification a fabric met, not necessarily who made the membrane or how it works. Where a brand does not publish those details, we do not infer them.

Sewing a garment punches a line of holes straight through the barrier. Gore's own guidance is blunt about it: seam tape seals the tiny holes created by sewing, the holes are small but can cause leaks, and Gore manufactures its own tape and regulates the taping process for compatibility and durability.

Seam tape is itself an engineered laminate. A seam-tape maker's technical guide describes a three-layer tape as an adhesive layer, a waterproof barrier film and a fabric backer, heat-activated onto the seam — and specifies different tape families for coated two-layer materials and for three-layer fabrics with a polyurethane membrane. Taping is a matched engineering decision, not a single universal product.

About the terms: fully taped or fully seam-sealed generally means every seam, and critically taped generally means only those the brand judges most exposed. Neither term is defined by a standard we could find, so what a given brand includes cannot be assumed from the phrase alone. EN ISO 24232 does bring seams within its scope and tests them, which is why professional rainwear specifications say more about seams than most consumer listings do.

The same logic extends past the seams. Hood geometry, cuff closures, hem adjustment, pocket placement and zip protection decide where water reaches you on a long day — and none of them is improved by a better membrane.