Today, we’re going to delve into the world of waterproof fabrics and examine exactly what the difference is between water-resistant and waterproof fabrics.
We’ll explore the science behind waterproof fabrics, highlighting the presence of breathable membranes and the hydrostatic head test. We will also touch upon the legal standards for waterproofness in different regions.
Whether readers are outdoor enthusiasts or simply curious about the topic, this guide is a must-read for anyone seeking to unveil the truth about waterproof gear.
- “Waterproof” beats “water resistant”!
- Legally, a fabric is waterproof if it withstands 1300mm (0.13 bar) in Europe, or 1500mm (0.15 bar) in the USA
- Water resistance is defined at 800mm (0.08 bar)
- For most outdoor pursuits we would recommend looking for 3000-5000mm.
- Don’t forget to check the quality of the zips and fasteners as these can easily be the source of leaks
- You will need to maintain the DWR coating on the face fabric to preserve the waterproofness.
In the past, when we thought about rainwear, we only considered whether it was waterproof. This essentially meant that rain couldn’t penetrate the fabric, thus keeping us dry. However, when we’re engaged in activities like cycling or hiking, we sweat. This meant the inside of the garment got wet, resulting in discomfort.
In response to this problem, the concept of breathable and waterproof fabric emerged. Over the years, these waterproof fabrics have evolved remarkably, moving from simple rainwear to advanced breathable, waterproof textiles.
This type of fabric contains a thin layer (or membrane) with tiny holes. These holes are big enough for sweat to pass but small enough to prevent water droplets from penetrating.
However this also means they cannot be entirely waterproof, but we can determine what pressure of water they will hold back, giving us a rating. Assessing the level of waterproofness and breathability in these fabrics is made possible by a procedure known as the hydrostatic head test.
Hydrostatic Head or Water Column
To understand how much pressure a fabric can withstand before water starts penetrating, we use a concept known as the ‘Hydrostatic Head’ or ‘Water Column’. This is simulated by filling a large tube with water, and at a certain point, the water pressure inside this tube becomes greater than the fabric’s resistance, causing the water to leak. The results of this test are expressed in millimeters of water.
However, it’s important to note that this test is not performed with a real water column as a 10m tall water column (which is 10,000mm after all!) is not really very practical. So instead it is simulated using a machine, specifically the Suter Tester, which was developed when Gore started making their Gore-Tex waterproof and breathable membranes.
The Suter Tester is a clever device comprising a water reservoir and a monometer to measure the pressure. As you pump air into the reservoir, the water pressure rises, pushing against the fabric sample. This helps to determine the fabric’s resistance to water penetration.
However, there are instances where the fabric may not be waterproof, especially at seams where wear and tear often occur. These areas can be easily tested using the Suter Tester to identify leaks.
Many outdoor gear shops have these, so if you think your jacket might be losing its waterproofing you may well be able to find one to test it.
What is the Legal Difference Between Waterproof and Water-Resistant Fabrics?
The difference between water-resistant and waterproof is legally defined; for water-resistant a minimum of 800mm or 0.08 bar, and for waterproof, 1300mm or 0.13 bar in Europe or 1500mm 0.15 bar in the USA. In other words, the difference between waterproof and water-resistant fabrics is 0.05 bar or 500 millimeters.
However, we would typically suggest looking for around 3000-5000mm for general outdoor activities. For strenuous activities like alpinism, where you’ll be carrying a heavy backpack, a higher rating of at least 10,000 mm is recommended.
To be considered waterproof under pretty much any circumstances beyond swimming, a rating of 20,000mm or above is needed.
Choosing the Right Gear
When selecting outdoor gear, it is crucial to carefully consider the appropriate options for your specific needs and activities. One of the most important factors to consider is the waterproofness of the fabric.
For activities like alpinism or carrying a heavy backpack, it is recommended to choose gear with a higher waterproofness rating, around 3000 millimeters or higher. On the other hand, for light rain or walking the dog, a lower rating of around 1000 millimeters may be sufficient.
To help you make an informed decision, here is a table that compares different waterproofness ratings and their recommended uses:
|Waterproofness Rating (mm)
|Light rain, walking the dog
|Light Hiking and backpacking
|Most Hiking and backpacking
|Alpine and Extreme conditions
|Pretty much anything
However, even with high waterproof ratings, common issues such as seam leakage and punctures can compromise the effectiveness of waterproof garments. Furthermore, the maintenance of the Durable Water Repellent (DWR) coating on the face fabric is paramount.
It is important to remember that even fabrics with a high waterproofness rating can be compromised if the seams or fabric surface is damaged. Damage to the fabric surface can significantly reduce the waterproofness of a garment.
If you see larger drops of water forming on the fabric, or bubbles forming on the fabric surface during the pressure test is a sign of damage. This damage can be caused by wear and tear or a damaged DWR coating.
You can usually repair damage to the DWR with either a wash and low-heat iron or re-applying the coating.
Common areas for damage to occur are in pressure points, for example, seams, pockets, or zippers. These areas should have a higher waterproof rating than the rest of the fabric.
Pressure points are areas on a garment that experience more strain than other parts, such as the elbows, shoulders, and knees. Also, because we naturally stretch the fabric by flexing our joints at elbows and knees, this also expands the holes in the fabric that give it its breathability, but make it less waterproof.
These areas of a garment may require increased waterproofness. So when selecting a waterproof garment, it is important to consider the level of waterproofness in the areas that will be exposed to the most wear and tear – so look for the weakest link and buy for this level.
Unfortunately, many manufacturers do not seal all seams but restrict sealing to the most vulnerable such as shoulder, elbow, and side seams. This is done with specific tapes, eg, welding heat-seal tape, or the use of adhesives on the inside to seal seams. Along with the sealing, checking the quality of the stitching is also extremely important.
Also, make sure that the manufacturer has not skimped on the zips and other fasteners as these can easily become the source of leaks and there is very little point having a 5000mm fabric with a 500mm zip…you’ll still get wet!
Generally, garments intended for outdoor activities like hiking should have a rating of at least 3-5,000 millimeters (preferably at the higher end), while garments for less intense activities may require a lower rating.
So, now you know what actually waterproof means, from a legal perspective, and how it differs from water-resistant. But as we discussed, it’s essential to consider your specific activity and conditions before selecting your outdoor gear. Your comfort and safety in the outdoors largely depend on these smart choices
And always remember to test your gear before a big trip and replace any items that are not effectively waterproof anymore.
Matt Green, is an avid hiker and lover of the great outdoors. He is always planning his next big trip or hitting the trails for a solo hike.
He’s traveled extensively to many remote regions and has plenty of experience exploring various terrains, and stories to tell.