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A waterproof rating in millimeters tells you how much water pressure a fabric can resist before water pushes through it. The number comes from a hydrostatic head test: the taller the column of water the fabric can hold back, the higher the rating, so a 20,000 mm fabric resists more pressure than a 5,000 mm fabric.
The number is only part of the story, though. Seams, zippers, coatings, breathability and how you use the garment all decide whether you stay dry. This explainer covers what the millimeter figure means, typical rating bands, how breathability ratings work, what changes in real use and how to compare jackets, pants and tents without overpaying for a number you do not need.
Key takeaways
- The mm figure is a hydrostatic head rating: the height of a water column the fabric resists before leaking.
- Higher numbers mean more resistance to water pressure, not that a garment is more waterproof in every way.
- Common rule of thumb bands run from light rain resistance at the low end to heavy, sustained rain at the high end.
- Taped seams, sealed zippers and a working water repellent finish matter as much as the fabric rating.
- Breathability is rated separately, often in grams of moisture per square meter per day or as an RET value.
- Match the rating to your conditions and activity rather than buying the highest number available.
What does a waterproof rating in mm mean?
A waterproof rating in mm, also called hydrostatic head, is the height of a column of water, in millimeters, that a fabric can support before water starts to seep through. A fabric rated 10,000 mm held back a 10 meter column of water in the test. The higher the figure, the more pressure the fabric can withstand.
The test is simple in principle. A sample of fabric is clamped under a tube, and water is added or pressure is increased until droplets appear on the other side. Laboratories use standardized methods, such as ISO 811 for textiles, so that results are measured in a consistent way.
Why pressure and not just rain? Because water rarely just sits on a jacket. It is pushed into the fabric by wind driven rain, by backpack straps pressing on your shoulders, by kneeling on wet ground or by sitting on a soaked log. Each of those raises the pressure on the fabric, which is why a higher rating can matter.
If you are new to outdoor gear numbers in general, our guide on how to read outdoor gear specs explains other common ratings you will see on labels.
What are typical waterproof rating ranges?
Typical waterproof ratings for outdoor fabrics run from a few thousand millimeters up to 20,000 mm and beyond. Retailers and brands commonly group them into bands, from light rain resistance at the low end to heavy, sustained rain at the top. These bands are a widely used rule of thumb rather than a formal standard.
| Rating (mm) | What it is commonly said to handle | Typical uses |
|---|---|---|
| Up to about 5,000 | Light rain or short showers, little pressure | Casual jackets, water resistant shells |
| About 5,000 to 10,000 | Light to moderate rain for limited periods | Everyday rain jackets, light hiking |
| About 10,000 to 15,000 | Moderate to heavy rain, some pressure | Hiking and travel shells, ski wear |
| About 15,000 to 20,000 | Heavy rain and more pressure | Backpacking, wet climates, mountain use |
| Above about 20,000 | Prolonged heavy rain and high pressure | Demanding mountain and expedition use |
Two points help put this table in context:
- Brands test differently. Two jackets both labeled 10,000 mm may not perform the same, because test methods, sample conditions and how long the test runs can vary.
- Water resistant is not waterproof. A low rating or a fabric with only a water repellent finish will shed a shower but can wet out in longer rain. Our explainer on waterproof vs water resistant clothing covers the difference in detail.
Tip: Look for whether a brand says how its rating was measured. A clear note on the test method is a better sign than a big number on its own.
How do breathability ratings work?
Breathability ratings describe how well a waterproof fabric lets sweat vapor escape from inside. They are usually shown as a moisture vapor transmission rate in grams per square meter over 24 hours, where higher is more breathable, or as an RET value, where lower is more breathable. Breathability matters because trapped sweat can leave you wet from the inside.
This is the trade off at the center of rainwear. A fully sealed plastic poncho is very waterproof but traps sweat. A breathable membrane or coating lets some vapor out while keeping liquid water out.
A few things to know:
- Two different scales. A figure in g/m2/24h and an RET value cannot be compared directly. Higher is better for the first, lower is better for the second.
- Test methods vary widely. Breathability results depend heavily on the method used, so comparing numbers across brands is less reliable than comparing waterproof ratings.
- Conditions change performance. In very humid air, breathable fabrics move less vapor because the outside air is already moist.
- Activity matters most. Hard uphill effort produces more sweat than any membrane can move. Venting and layering do much of the work.
Good layering under your shell makes a big difference. A base layer that moves moisture well helps the whole system, and our comparison of merino wool vs synthetic base layers explains how each handles sweat.
What else affects whether a waterproof jacket keeps you dry?
Whether a waterproof jacket keeps you dry depends on more than the fabric rating. Fully taped seams, water resistant or covered zippers, a well designed hood, a working durable water repellent finish and a good fit all play a part. A high rated fabric with untaped seams can still leak, because water gets in through the stitching.
Seams and zippers
Stitching punches small holes in fabric. Waterproof garments cover the inside of seams with tape. Look for “fully taped” or “fully sealed” seams rather than “critically taped,” which can mean only the shoulders and hood are covered. Zippers should be water resistant or protected by a storm flap.
Durable water repellent finish
Most shells have a durable water repellent (DWR) finish on the outside that makes water bead and roll off. When it wears off, the outer fabric soaks up water, known as wetting out. The jacket may still block water, but it feels clammy and breathes poorly. Washing and reproofing as the care label directs can restore it.
Fabric construction
Waterproof fabrics are often described by their layers:
| Construction | What it is | Common trade offs |
|---|---|---|
| 2 layer | Outer fabric bonded to a membrane, with a separate hanging liner | Comfortable, can be heavier and bulkier |
| 2.5 layer | Outer fabric and membrane with a thin printed protective layer inside | Light and packable, can feel clammy |
| 3 layer | Outer fabric, membrane and inner fabric bonded together | Durable and good for hard use, often costs more |
Membranes such as Gore-Tex are well known examples of the technology, and many brands use their own membranes or coatings. The construction, not just the brand of membrane, shapes how the garment feels and lasts.
Fit and design
A hood that turns with your head, cuffs that seal, a hem that covers your waist and enough room for layers all help keep water out. For a full walk through on features, see our guide on how to choose a rain jacket.
How much waterproof rating do you actually need?
The waterproof rating you need depends on how long you will be out in rain, how heavy the rain tends to be and how much pressure your gear will face. For short walks in occasional showers, a modest rating can be enough. For long hikes in wet climates, with a pack and wind, a higher rating gives more margin.
Use this as a simple guide:
| Use | Conditions | Rating to consider |
|---|---|---|
| City walking and travel | Short showers, easy shelter | Lower to mid range |
| Day hiking | Occasional rain, a few hours out | Mid range |
| Backpacking | Longer exposure, pack straps add pressure | Mid to higher range |
| Wet climates and mountains | Heavy, sustained rain and wind | Higher range |
| Skiing and snowboarding | Wet snow, sitting on lifts | Mid to higher range |
Higher ratings can come with trade offs, such as a stiffer feel, more weight or a higher price, though modern fabrics vary. Buying the highest number available is not always the best choice. A well built jacket with a sensible rating, sealed seams and good ventilation often serves better than a top rated fabric with poor design.
Weather also changes quickly in the outdoors. Our guide on how to prepare for changing trail weather explains how to plan layers and rain gear for days that start dry and turn wet.
How do waterproof ratings apply to pants, boots and tents?
Waterproof ratings apply across outdoor gear, but the pressure each item faces differs. Rain pants face pressure at the knees and seat, boots rely on membranes and seams that are rarely rated in millimeters, and tents typically list one rating for the rainfly and a higher one for the floor, because your body weight presses the floor into wet ground.
- Rain pants and hiking pants: Kneeling and sitting raise pressure, so look at the rating and seam sealing. Most hiking pants are not waterproof at all and rely on quick drying fabric. Our guide on how to choose hiking pants covers the options.
- Boots and shoes: Waterproof footwear usually uses a membrane bootie. Look for clear claims about the membrane and seam construction rather than an mm figure.
- Tents: Floors usually carry a higher rating than the fly because they are pressed into the ground. A footprint can add protection. The rating is one factor alongside design, seams and pitching.
- Bags and packs: Many packs are water resistant rather than waterproof. A pack liner or rain cover is often the reliable answer.
What about IP ratings?
IP ratings, such as IPX4 or IPX7, are a different system used mainly for electronics like headlamps and phones. They describe protection against splashes or immersion under defined test conditions rather than a fabric’s resistance to pressure. Do not compare an IP rating with a millimeter rating on clothing.
How do insulated jackets fit with waterproof ratings?
Insulated jackets are usually not waterproof unless they have a waterproof shell fabric with taped seams. Most fleeces and puffy jackets are designed for warmth, not rain, and depend on a rain shell over the top in wet weather. Down insulation loses warmth when wet, while synthetic insulation keeps more of it, which affects your choice.
In a layering system, the waterproof shell is the outer layer, the insulation is in the middle and the base layer sits next to your skin. Our guides to outdoor clothing layering basics and fleece vs puffy jacket show how these pieces work together so you are not relying on one garment to do everything.
What are common mistakes when comparing waterproof ratings?
Common mistakes when comparing waterproof ratings include treating the mm figure as the only measure that matters, comparing breathability numbers measured by different methods, ignoring seam taping, neglecting care of the water repellent finish and buying far more rating than your trips need. Avoiding these leads to better choices and drier days.
| Mistake | Why it misleads | Better approach |
|---|---|---|
| Choosing by rating alone | Seams and design can let water in | Check seams, zippers and hood too |
| Comparing breathability across brands | Test methods differ | Compare within one brand or by reviews of feel |
| Assuming water resistant means waterproof | Shells wet out in long rain | Check for a rating and sealed seams |
| Never washing or reproofing | DWR fails and fabric wets out | Follow the care label |
| Buying the highest rating available | May add stiffness, weight or cost | Match the rating to your conditions |
| Ignoring ventilation | Sweat soaks you from inside | Look for pit zips and adjustable vents |
Frequently asked questions
Is 10,000 mm waterproof enough?
For many hikers and travelers, a 10,000 mm rating is commonly considered enough for light to moderate rain over a few hours, especially with fully taped seams. For long days in heavy, wind driven rain, or when a pack presses on your shoulders for hours, a higher rating gives more margin.
What does 20,000 mm waterproof mean?
A 20,000 mm rating means the fabric resisted a 20 meter column of water in a hydrostatic head test before leaking. It is generally considered suitable for heavy, sustained rain and higher pressure from packs and kneeling. Seam taping, zippers and fit still decide whether the whole garment keeps you dry.
Why does my waterproof jacket feel wet inside?
A jacket can feel wet inside because of sweat condensing under the shell, especially during hard effort or in humid weather. It can also happen when the outer water repellent finish has worn off and the fabric wets out, reducing breathability. Venting, lighter layers and reproofing help. Leaks at seams or zippers are another possible cause.
Is a higher waterproof rating always better?
Not always. A higher rating resists more water pressure, but it can come with trade offs such as a stiffer feel, more weight or a higher price. If you mostly walk in short showers, a modest rating with good seams and ventilation may serve you better than the highest number available.
What is the difference between waterproof and breathability ratings?
A waterproof rating in mm measures how much water pressure a fabric resists from outside. A breathability rating measures how much sweat vapor can pass out through the fabric from inside, often in grams per square meter per day or as an RET value. Good rainwear balances both for your activity.
Featured photo: pixellaphoto via Openverse (CC0).
