Getting wet is a natural consequence of spending time on the water. You’ll never be able to avoid water completely (and we highly doubt that you want to), whether it’s sitting on a damp deck or dealing with spray at speed.
However, there’s always a balance to strike. As a sailor, you’re never completely separate from the environment and yet the right waterproof gear is one of the most important things you rely on. Take your jacket or drysuit as an example. They’re both essentials in so many different conditions and act as a first line of defence to stop the exposure that you will inevitably encounter from becoming a problem.
Waterproof ratings provide a uniform way to define how well this equipment performs, usually as a single number that you don’t really know the meaning of, beyond knowing they’re important. We’ve broken this down in this guide, explaining what waterproof ratings are, how they’re measured and what you need to look for.
What Is A Waterproof Rating?
A waterproof rating is a standardised measure of how well a fabric can resist water passing through it. You’ll see it referenced across a range of products, both in the world of sailing and beyond, including waterproof jackets, waterproof trousers, and drysuits.
In simple terms, the higher the waterproof rating, the more waterproof the fabric. However, when it comes to high-performance equipment, there is a little more nuance. Waterproof ratings are based on controlled testing and aren’t the only way to determine how useful a garment will be in wet conditions (but more on that shortly…).
How Are Waterproof Ratings Measured?
Waterproof ratings should never vary from manufacturer to manufacturer and instead are measured through something called a hydrostatic head (HH) test. This measures how much water pressure any fabric can withstand before it leaks.
During a hydrostatic head test, a column of water is placed over the tested fabric and pressure is gradually increased. The point at which water passes through determines its rating. For example:
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A waterproof jacket that can withstand the pressure of a 30-metre column of water before failing has a 30,000mm waterproof rating.
The main reason why waterproof fabrics are tested in this way is that the HH test is good at representing the strain they might come under during real use.
What Do Waterproof Ratings Mean?
It can be really reassuring to know that your waterproof clothing has been properly tested and rated, but these numbers still don’t mean much if you don’t know what they mean in real terms.
There’s not necessarily such a thing as a ‘good’ waterproof rating in the sense that it’s better to relate different ratings to how well they perform in different conditions. You might not need the highest rating if you’re just exposed to some light rain, but if you’re extremely exposed, then this is unlikely to be ‘good’ enough.
Waterproof Rating |
Typical Use |
| 5,000 to 10,000mm | Light rain and short-term exposure |
| 10,000 to 20,000mm | Sustained rain and regular use |
| 20,000mm + | Heavy weather and extended time on the water |
| 30,000mm + | Offshore sailing and extreme conditions |
Other Key Elements Of Waterproofing
A high waterproof rating gives you more margin and protection, but is only one part of the picture. Think of your rating as a reference point alongside the following components of any garment.
Breathability
Water getting into a garment is just one kind of moisture you need to consider. Your body creates moisture, too, in the form of heat and sweat. Over time, this can cause your clothing to become damp, which feels pretty similar to any water that could get in from the outside. As a result, breathability is as important as waterproofing, and a well-balanced fabric will both keep external water out while allowing internal moisture to escape.
Fabric Construction
It’s rare that any piece of waterproof sailing clothing, particularly one with a solid waterproof rating, will be made from a single-layer fabric. The best waterproof fabrics are made up of multiple layers that work together, such as an outer fabric bonded to a waterproof membrane, often with an additional inner lining.
Seams are critical, too. Even a highly waterproof fabric can fail if water can seep in through the stitching. That’s why, at Gill, taped seams are standard across our gear.
How Gill Tests Waterproof Performance
A waterproof rating gives you a really clear baseline of how strongly a fabric can perform, but it doesn’t go beyond this and tell you how well a fabric will hold up once worn and when exposed to the kind of conditions sailors encounter.
That’s why our fabrics are tested beyond standards, with testing running through the entire development process, where we develop materials specifically for the marine environment. Hydrostatic head tests form part of that process, with our XPLORE® and XPLORE+® technologies reaching 20,000mm and 30,000mm respectively. However, we also test how well moisture escapes, how our fabrics respond to abrasion against deck-like surfaces, and how DWR finishes cope with constant water exposure.
Event trims and components are tested for corrosion resistance to ensure that no single point causes the fabric to fail. Ultimately, it’s our goal to test our fabrics in a way that reflects how it’s actually used and not just how it performs in isolation, giving you complete confidence that your gear will perform when you need it most.
