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You are looking for a new rain jacket and comparing two models. One has a hydrostatic head rating of 10,000 mm, the other 20,000 mm. Both cost about the same and look similarly robust at first glance. But what does this number actually tell you? Hydrostatic head is one of the most important technical values when it comes to how reliably outdoor clothing keeps water out.
To help you understand hydrostatic head ratings for rain jackets, we explain what the value means, when a rain jacket can really be considered waterproof, and which rating makes sense for different activities. You will also find out what to look for in winter jackets, ski pants, kids’ clothing and tents.
Key Takeaways
- 💧 Hydrostatic head indicates how much water pressure a fabric can withstand before water starts to penetrate. The higher the value in millimetres, the more waterproof the material is.
- 🌧️ For rain jackets, 10,000 mm hydrostatic head is a solid benchmark for hiking, everyday use, running and cycling in normal conditions.
- 🎒 In persistent rain, with a heavy backpack or on multi-day tours, 20,000 mm hydrostatic head or more is a sensible choice, as shoulder straps and pack weight increase pressure on the fabric.
- 🧵 A high hydrostatic head alone does not make a jacket reliably waterproof. Taped seams, protected zips, the right fabric construction and an intact water-repellent finish are just as important.
- 🏕️ Tents also need to be chosen according to their intended use. Around 3,000 mm is a useful guideline for a flysheet, while a tent floor should offer at least 5,000 mm due to the higher pressure from body weight and contact with wet ground.
What Does Hydrostatic Head Mean?
Hydrostatic head is a measurement of how much water pressure a material can withstand before it starts to leak. It is given in millimetres, for example 10,000 mm hydrostatic head or 20,000 mm hydrostatic head. The number describes how high a column of water could stand on that exact fabric before water begins to push through at the bottom. The higher the value, the more pressure the fabric can handle.
For rain jackets, hydrostatic head is measured using what is commonly known as the Suter test. A fabric sample is exposed to increasing water pressure from the outside. Depending on the standard used, the pressure rises in increments of 100 to 600 mm hydrostatic head per minute. As soon as three drops of water become visible on the inside, the test ends. The pressure measured at that point is the stated hydrostatic head rating.
Important to know: hydrostatic head is a guideline, not an absolute guarantee. Different standards, such as the European ISO 811 and the US AATCC 127, can produce different results because the test setup and sometimes the ageing of the material vary. This means that two jackets with the same hydrostatic head rating may perform differently in practice if they were tested according to different standards.
Hydrostatic Head and Breathability: A Trade-Off
The more effectively a fabric blocks water from the outside, the harder it usually is for water vapour to escape from the inside. As hydrostatic head increases, breathability often decreases, which you may notice as sweat build-up during high-output activities. High-quality membranes such as GORE-TEX or Sympatex are designed to offer reliable waterproof protection while still allowing a reasonable level of breathability. Even so, no technology can completely eliminate this trade-off.
What Hydrostatic Head Rating Should a Rain Jacket Have?
For rain jackets, 10,000 mm hydrostatic head has become a common benchmark in the outdoor world. This rating is suitable for hiking, running and cycling in normal conditions, even during longer periods of rain. Most established hardshell models are already well above the legal minimum for “waterproof” and therefore offer a useful safety margin.
If you are hiking with a heavy backpack or expect continuous rain on a multi-day trip, a rain jacket with 20,000 mm hydrostatic head or more is the better option. The reason is pressure. Backpack straps press wet sections of fabric against your shoulders and back, creating much higher local stress than you would have without heavy gear. A higher hydrostatic head gives you the extra protection you need before moisture starts to push through.
What Else to Look for When Buying a Rain Jacket
Hydrostatic head describes the fabric or membrane, but not automatically every potential weak point in the finished jacket. A high rating alone does not instantly make a jacket a reliable rain jacket. The material can only perform at its best when combined with well-finished seams, a suitable fabric construction and regular care. Here are the most important things to consider when buying a rain jacket, alongside its hydrostatic head rating:
- Seams: Only waterproof welded or taped seams prevent water from entering through the stitch lines and panel joins.
- Zips: Waterproof or well-covered zips are especially important in wind-driven rain and exposed conditions.
- Fabric construction: For everyday use, 2-layer constructions made from an outer fabric and membrane are usually sufficient. Under heavier use, however, they can feel slightly clammy. A heavier 3-layer jacket is the better choice if you carry a heavy backpack or spend long days outdoors. In a 3-layer construction, the membrane is fully bonded between a robust outer fabric, the hardshell, and an inner lining. This makes the material more stable and abrasion-resistant on the outside, while also improving breathability.
- DWR finish: An intact DWR finish makes water bead off the outer fabric and helps maintain breathability, but it wears off with use and washing. DWR stands for Durable Water Repellent. Unlike the membrane, it is an additional water-repellent treatment that wears down over time and needs to be refreshed.
💡 Our tip:
When choosing rain jackets and other weatherproof clothing, go for high-quality outdoor brands. They usually pay attention not only to strong material ratings, but also to cleanly taped seams, functional zips, well-designed fabric constructions and durable water-repellent finishes.
What Hydrostatic Head Rating Should Rain Pants Have?
For rain pants, the recommended benchmark is higher than for rain jackets, at around 15,000 mm hydrostatic head. The reason is easy to understand from a mechanical perspective. When you sit, kneel or wear a hip belt, much more body weight is concentrated on a smaller area, which greatly increases local pressure on the fabric. If the hydrostatic head is too low, pants will usually start to leak first at exactly these stress points.
For activities with frequent ground contact, such as sitting in wet grass during breaks or moving through alpine terrain with a loaded pack, rain pants with 20,000 mm hydrostatic head are worth considering. If you only wear them in moderate rain for everyday use, 15,000 mm hydrostatic head is usually enough.
Hydrostatic Head Chart: Guidelines for Jackets, Pants and Tents
Not every piece of clothing needs the same hydrostatic head rating as a robust trekking rain jacket. What matters is not only how hard it rains, but also how much pressure is placed on the material. Sitting on wet ground can already create pressure equivalent to around 2,000 mm hydrostatic head. Kneeling can generate around 4,800 mm.
The right rating therefore depends on the product type and intended use. A lightweight winter jacket for everyday wear often needs less protection than a hardshell for long tours, while rain pants, ski clothing and tent floors are exposed to higher pressure through sitting, kneeling or contact with wet ground. The following chart gives you practical guidelines for different product groups and activities.
| Product | Recommended hydrostatic head | Best for |
|---|---|---|
| Rain jacket | From 10,000 mm | Suitable for hiking, running and cycling in everyday use, without heavy gear pressing on the fabric |
| Rain jacket with backpack / hardshell | From 20,000 mm | Useful in continuous rain, with heavy gear and on multi-day tours |
| Rain pants | From 15,000 mm | Higher pressure from sitting, kneeling and concentrated stress points |
| Winter jacket for everyday use | From 5,000 mm | Sufficient for snow and occasional rain in daily use |
| Ski jackets and ski pants | From 15,000 mm | Stress from falls, sitting in snow and chairlift rides |
| Kids’ clothing, such as snowsuits and rainwear | From 4,000 mm | Kids often sit, kneel and play in wet conditions, but are usually not exposed for days at a time |
| Tent flysheet | From 3,000 mm | Lower pressure than on the floor, but continuous exposure to rain and wind |
| Tent floor | From 5,000 mm | Body weight while kneeling creates high local pressure |
When Is a Material Considered Waterproof?
The international standard EN ISO 24232 replaces the previous EN 343 standard and defines requirements for protective clothing against rain. Among other things, it assesses resistance to water penetration and breathability. Waterproof performance is divided into classes, with higher classes indicating better protection against water entering the material.
Under the earlier EN 343 standard, comparatively low values were already considered waterproof. The Swiss materials testing institute EMPA applies a stricter benchmark and classifies functional fabrics as waterproof from 4,000 mm hydrostatic head. For outdoor clothing in real-world use, however, these minimum values are only a rough guide. Whether a jacket will keep you reliably dry in continuous rain, wind, movement or with a backpack also depends on its construction, seams, zips, fabric layers and care.
In practice, higher guideline values are more useful. For rain jackets, around 10,000 mm hydrostatic head is a good benchmark for many everyday and outdoor activities. For rain pants, hardshells, ski clothing or tours with a heavy backpack, 15,000 to 20,000 mm or more is often the better choice.
Conclusion and the Right Gear
For most hiking and outdoor activities, a rain jacket with 10,000 mm hydrostatic head is more than enough. If you are carrying heavy gear or heading out in persistent rain, 20,000 mm is worth it. Rain pants need a little more reserve because of the higher pressure created when sitting and kneeling. If you want to be on the safe side, choose pants with at least 15,000 mm. In the end, reliable weather protection always depends on the full package: hydrostatic head, workmanship and care.
You can find suitable rain jackets with the right hydrostatic head rating in our rain jacket range, and robust rain pants are also available directly from the Sport Conrad shop.