What is waterproof?
How it differs from water repellent and water resistant
Three words that sit side by side in every shop listing and do not mean the same thing. Two of them stand for a test standard of their own, the third stands for none. This page explains what each one actually measures, which figures our fabrics reach and what decides on a finished product whether it stays dry.
Three words that do not mean the same thing
The difference is not a matter of degree. It lies in what is being tested at all. Two of the terms stand for a measurement, one stands for nothing measurable.
Water repellent describes the surface
The fabric carries a finish that makes water bead up on the face instead of soaking in. This is assessed with the spray test to ISO 4920 and graded from 0 to 5. The weave itself stays open and breathable, because the finish sits on the fibre. The technical name is hydrophobic finishing, in everyday language it is called impregnation.
Waterproof in one sentence
A fabric is waterproof when it withstands water pressure without letting it through. That is measured as a water column to ISO 811 and stated in millimetres. It is not achieved by a finish but by a closed layer: a backing laminate or a coating.
Water resistant is not a test term
Textile testing has no method, no scale and no unit for water resistant. In everyday use the water resistant meaning is simply that an item survives contact with water. It says nothing about whether water passes through.
Why the distinction matters when buying
A water repellent cover sheds summer rain and dries quickly again. A waterproof cover also holds back standing water and pressure, but it weighs more and needs openings to breathe. So the question is not which is better, but which suits the location.
Two tests, two different questions
Both methods come from the same ISO textile committee, TC 38 subcommittee SC 2. They still do not answer the same question, and neither replaces the other.
| Feature | Spray test to ISO 4920 | Water column to ISO 811 |
|---|---|---|
| What is measured | whether the face of the fabric gets wet | what water pressure the fabric withstands |
| Test setup | 250 ml of water run from a nozzle onto a specimen inclined at 45 degrees, taking 25 to 30 seconds | water pressure over an area of 100 square centimetres is raised steadily |
| End point | immediately after spraying the holder is tapped and the face is rated | the pressure at the moment water penetrates in the third place |
| Result | a grade from 0 to 5, where 5 means no wetting of the face | a pressure in millimetres of water column, 1,000 mm being roughly 98 millibars |
| Specimens | at least three, each at least 180 mm square | at least five, taken from different places in the fabric |
| What the standard itself rules out | it states that it is not intended to predict rain penetration, because it does not measure penetration at all | it names no threshold and no classes at which a fabric may be called waterproof |
Water resistant, and why we avoid the word
Neither ISO 4920 nor ISO 811 nor any other textile standard defines the term. Calling a fabric water resistant quotes no measurement. It still appears in descriptions all the time, usually as a catch-all for everything between beading and sealed. That vagueness is exactly why we leave it out.
We call a fabric water repellent when it reaches 5 out of 5 in the spray test and carries no backing laminate. We call it waterproof when a laminate or coating closes it and it therefore reaches at least 1,000 mm water column. That is a rule of our own house along the manufacturers' figures, not a requirement of any standard. How the millimetre figure comes about is explained on What is a water column?.
Figures such as 1,500 mm come from product standards for specific product groups, the best known being EN 343 for protective clothing against rain. There the fabric is pre-treated in a defined way before measuring, that is washed, abraded and creased, and only the figure obtained afterwards decides the class. None of that transfers to cushions, shade sails and covers, because neither the pre-treatment nor the stress is the same. Pure cover fabrics such as Cover PVC sit far above those figures anyway at 4,000 mm.
Waterproof fabric and water repellent fabric in our range
The figures come from the manufacturers' technical data sheets. Where a figure is not stated there, it says so here instead of being estimated.
| Fabric | Spray test | Water column | Classification |
|---|---|---|---|
| Agora Liso, Lines, Rayure, Panama, Life Liso | 5 out of 5 | 180 mm | water repellent, open weave without laminate |
| The same fabrics with PU laminate | 5 out of 5 | 1,000 mm | waterproof, the laminate adds 44 g per square metre |
| Agora Liso Waterproof, listed as weatherproof in our shop | 5 out of 5 | 1,000 mm | waterproof, releases 240 to 320 g of water vapour per square metre in 24 hours |
| Sunbrella Natté | 5 out of 5 | not stated by the manufacturer | water repellent |
| Polysun | 4 out of 5 | not stated by the manufacturer | water repellent, one grade below the Agora qualities |
| Dralon Acrisol Liso | not quantified, listed as hidrofugo on the data sheet | 1,000 mm with laminate on request | water repellent, waterproof when laminated, the laminate is not a stock item |
| Cover PVC | not applicable, the surface is coated | 4,000 mm | waterproof, the highest figure in our range |
| swela vuscreen Livorno | water repellent finish | not applicable | screen fabric, deliberately permeable through its perforation |
What actually decides on a finished product
Both tests measure a piece of new fabric under laboratory conditions. A cover on a terrace lives under different ones, and four of those weigh more than the figure itself.
The seam is the real limit
Every needle hole breaks through the coating. A cover made from laminated fabric only becomes sealed once the seams are taped as well. That sealing needs build height and can only be executed cleanly from 6 cm cushion thickness upwards. Which seam types we produce is shown in our overview of cushion seam types.
Impregnation wears off, and can be renewed
Sun, dirt and cleaning wear the finish away. A fabric that scored 5 out of 5 when new beads less well after a few seasons. Re-impregnating restores most of the water repellency. A backing laminate ages differently: it stays sealed, but tolerates neither full sun nor a pressure washer.
Drying out beats sealing
Under prolonged wet weather it matters less how much water the fabric holds back than whether the product can dry again. That is why waterproof seat pads get air holes for pressure equalisation, and why a water repellent cover in an airy spot is often the better choice than a sealed one.
Pressure from above is not test pressure
Sitting down on a wet cushion creates several times the pressure used in the laboratory, concentrated on a small area. A high figure is therefore no promise for every situation, it is a statement about the fabric under defined conditions. How we solve this on finished covers is shown by our weatherproof cushions.
Frequently Asked Questions
Sources
- ISO 4920:2012, Textile fabrics - Determination of resistance to surface wetting (spray test). Freely available standard preview covering scope, test setup, number of specimens and the complete rating scale from 0 to 5
- Catalogue entry for ISO 4920:2012, noting the superseded first edition of 1981
- ISO 811:2018, Textiles - Determination of resistance to water penetration - Hydrostatic pressure test. Standard preview with the test principle, test area and end point
- What is a water column? The measure behind every waterproof claim
- All Germes fabrics with their technical figures
Last reviewed: 24.08.2026 · Reviewer: Germes-Team
Water repellent or waterproof: which suits your location?
Tell us where the product will stand, whether it is under cover and how often it gets wet. We will tell you which of the two versions makes sense and which one you can save yourself.