What Is a Waterproof Coating?

How is a waterproof coating made?

A waterproof coating is made by spreading a liquid polymer over one face of a fabric and letting it set into a continuous film that water cannot cross. In 1823 the Scottish chemist Charles Macintosh dissolved rubber in coal-tar naphtha, painted it onto wool cloth and laid a second layer of wool on top, and the raincoat called the mackintosh is named after him.

Early rubber cloth went stiff in winter and sticky in hot weather, and tailors punctured it when sewing seams. Vulcanised rubber, which coped better with temperature changes, arrived in 1839. Museum conservators now deal with polyurethane coatings on cotton, knits and leather. Coated leathers such as patent leather have their own entry, and cloth coated with PVC is covered under vinyl (PVC).

Coating, membrane, water-repellent finish: what is the difference?

Wax is one of the water-repellent finishes, which is why waxed canvas belongs with the water-repellent finishes rather than with coated cloth. Densely woven fabrics take a fourth route: a 2023 review in the journal Materials describes high-density cloths whose tiny gaps between yarns resist wind and rain without any film. Weave density is covered under gabardine.

What are the properties of a waterproof coating?

A waterproof coating keeps out liquid water but lets little water vapour escape, so sweat vapour can build up inside a coated garment. The same review sums up waterproof-coated fabrics in exactly those terms: excellent water resistance, poor water vapour permeability.

Breathable membranes fall mainly into two kinds:

• Hydrophilic (non-porous) membranes have no pores. Water molecules are adsorbed on the humid side, move through the film and are released on the drier side.
• Microporous membranes, such as stretched PTFE, are full of tiny connected pores. They block water droplets, which are over 100 μm across, but let through vapour molecules under 1 nm. Their pores can become polluted and blocked, which cuts breathability.

How is waterproofness measured?

Waterproofness is measured by hydrostatic head: water pressure is applied to the face of the fabric and raised gradually until water comes through, and the higher the pressure the fabric withstands, the better its water resistance. Results are given in pascals (Pa) or millimetres of water; 1,000 Pa is roughly 102 mm.

The 2023 Materials review gives 9.8 kPa (about 1,000 mm) as the minimum acceptable hydrostatic pressure for sportswear and raincoats. Surface repellency is a separate property, measured by the angle a water drop makes with the fabric; above 150° the surface is called super-hydrophobic.

The EN 343 classes

In Europe, protective clothing against rain is rated under EN 343, which sets four water-penetration classes:

• Class 1: fabric and seams are tested as new and must withstand more than 8,000 Pa.
• Class 2 and above: fabric is also tested after pre-treatments that include abrasion, flexing, exposure to fuel and oil, and laundering; the top classes demand higher pressures.

EN 343 has a separate set of four breathability classes, from 1 to 4, where a higher number is better.

How do you tell a good waterproof coating from a poor one?

Judge a waterproof coating by its tested rating, its seams and the state of the film itself.

• Read the class, not just the word. If a garment is rated to EN 343, a water-penetration class of 2 or higher means the fabric passed after abrasion, flexing and laundering; Class 1 means it was tested only as new.
• Turn it inside out and check the seams. Stitching punctures the coating or membrane, the problem Macintosh's tailors met. EN 343 tests seams as well as fabric, and SATRA's guide to the standard stresses correct seam-sealing techniques. Unsealed stitching on a coat sold as waterproof is a red flag.
• Look at the pockets and openings. EN 343's optional cloudburst test checks whole garments because design faults, such as pockets that fill with water, let rain in even when the fabric holds.
• On vintage or second-hand pieces, press and flex the coated side. Tackiness, cracks running through the film, flaking, peeling from the base cloth or a white powdery bloom all point to a breaking-down coating. The bloom on polyester-based polyurethane comes from its reaction with moisture. Flaking is worse on flexible knit bases such as jersey.

How do you care for a waterproof coating?

Care for a waterproof coating by keeping it clean, washing it only as the care label directs, and storing it cool and dark. The 2023 Materials review notes that washing damage to a fabric's waterproof and breathable properties is permanent.

Heat harms coatings too. Rubber went sticky in hot weather, and ester-based polyurethane is sensitive to heat ageing and hydrolysis (breakdown by moisture), while ether-based types resist hydrolysis better but suffer more from light. For long-term storage, MoMu's conservators describe oxygen-free (anoxic), cool, dark storage at 40–50% relative humidity as showing promise.

Is a waterproof coating sustainable?

Whether a waterproof garment is sustainable depends on its chemistry, and the part EU law now limits is PFHxA and related substances, one group of fluorinated chemicals. Older water-repellent (DWR) finishes were side-chain fluorinated polymers with long perfluoroalkyl chains, replaced after the phase-out of long-chain PFAS (per- and polyfluoroalkyl substances).

A 2016 review in Environment International grouped the alternatives as side-chain fluorinated polymers, silicones, hydrocarbons and other chemistries, including dendrimers and inorganic nanoparticles. It found that impurities or degradation products of all of them are released into the environment, and that non-fluorinated finishes lack oil repellence. Of the groups assessed, the authors judged hydrocarbon-based DWR the most environmentally benign.

In the EU, under Commission Regulation (EU) 2024/2462, textiles in clothing and related accessories for the general public may not, from 10 October 2026, be placed on the market with PFHxA and its salts at 25 ppb or more, or PFHxA-related substances at 1,000 ppb or more. Other consumer textiles follow from 10 October 2027. The regulation names rain jackets as covered clothing. For other textiles, such as carpets and upholstery, it notes that alternatives for water repellency appear to be available. As of 2026, it exempts certain category III personal protective equipment.