A garment is waterproof when four things work together: a fabric or membrane that water can't push through, seams that have been sealed shut, a water-repellent finish on the outside face, and openings - zips, hood, cuffs, hem - that don't let water in the back door. Miss any one of them and the jacket leaks, no matter how good the number on the swing tag is.
Most people buy a rain jacket by looking at one figure: the mm rating. It matters, but it's one of four things, and on its own it tells you surprisingly little. Here's what each part actually does, what the numbers mean, and how to tell whether a jacket will hold up before you've stood in the rain for three hours finding out.
What does the mm waterproof rating actually mean?
The mm rating is a hydrostatic head measurement. It's the height of a column of water the fabric can hold back before water forces its way through.
Under ISO 811, the international test standard, a fabric sample is clamped under a sealed tube of water and the pressure is raised at a steady rate - 100mm of water column per minute for standard testing. The test ends the moment three droplets appear on the other side. Whatever the pressure was at that point, in millimetres of water, is the rating.
So a 10,000mm fabric held back a ten-metre column of water before it gave up. That sounds absurd for something you'll wear in drizzle, and it would be - except rain isn't the pressure that matters.
What matters is localised pressure: a pack strap grinding into your shoulder, kneeling on wet ground to gut a deer, sitting on a damp log, an elbow pressed into a wet fence rail, wind driving rain sideways into your chest. Those generate pressures far beyond anything falling rain does. That's the real reason a jacket needs a high number - not the rain itself, but you pushing the wet fabric against your body.
Waterproof ratings, in plain terms
| Rating | What it handles | Realistically |
|---|---|---|
| Under 1,500mm | Light drizzle, brief exposure | Water-resistant, not waterproof. A windbreaker. |
| 1,500-5,000mm | Light rain, low activity | Fine walking the dog. Not fine on a ridgeline. |
| 5,000-10,000mm | Steady rain, moderate activity | The point where a jacket becomes genuinely useful outdoors. |
| 10,000-15,000mm | Sustained heavy rain, pack straps, kneeling | The practical sweet spot for New Zealand conditions. |
| 20,000mm+ | Extreme and alpine exposure | Real, but you pay heavily for headroom most people never use. |
1,500mm is the figure most commonly cited as the threshold at which a fabric can reasonably be called waterproof rather than water-resistant. It's a floor, not a target.
For reference: our Outlander Waterproof Jacket is rated at 10,000mm. That's chosen deliberately - enough to sit down, kneel, and carry a loaded pack in sustained rain without water being pushed through, without paying for expedition-grade overkill you'd never call on.
Why breathability matters as much as the waterproof rating
Here's the part the swing tag rarely explains. You can be soaked through inside a jacket that has not leaked a drop.
A working adult puts out somewhere between half a litre and a litre of sweat an hour walking uphill under load. If that vapour can't get out, it condenses on the inside of the shell and runs down your back. You end up wet, cold, and convinced the jacket has failed. It hasn't. It's just sealed you in.
Breathability is usually given as MVTR - moisture vapour transmission rate - in grams of water vapour passing through a square metre of fabric in 24 hours.
| MVTR (g/m²/24hr) | Suits |
|---|---|
| Under 5,000 | Standing around. Fishing, spectating, sitting in a hide. |
| 5,000-10,000 | Walking, general outdoor use, farm work at a steady pace. |
| 10,000-15,000 | Hiking uphill, hunting on the move, sustained physical work. |
| 20,000+ | Running, ski touring, anything with your heart rate pinned. |
The number to look for is a balanced pair. A jacket rated 20,000mm waterproof and 3,000g breathable will keep the rain out and cook you. The Outlander runs 10,000mm / 10,000g - matched, on purpose, for people who are moving rather than standing still.
One caveat worth knowing: MVTR test methods vary between manufacturers, so comparing a number from one brand to another isn't as clean as it looks. Treat it as a band, not a decimal place.
Membranes, coatings and what "layers" means
The waterproof part of a jacket is either a membrane (a thin film laminated to the fabric, riddled with pores too small for liquid water but big enough for water vapour) or a coating (a polyurethane layer applied directly to the fabric's back). Membranes generally breathe better and last longer. Coatings are cheaper and can perform well when done properly.
Layer counts describe how that sandwich is built:
- 2-layer - face fabric + membrane, with a loose mesh or fabric liner hanging inside. Common, comfortable, bulkier.
- 2.5-layer - face fabric + membrane + a thin printed protective coating instead of a liner. Lightest and most packable, and the clammiest against skin.
- 3-layer - face fabric + membrane + a backing fabric bonded to it. The most durable construction and the standard for hard use.
Don't read a higher layer count as automatically better. What decides how a shell performs is how well the laminate is bonded, what membrane sits inside it, and what face fabric protects the lot. The Outlander is built around a ripstop face fabric - a reinforced grid weave where a tear that starts is stopped by the next thread in the grid rather than running the length of the panel. That matters more than most specs when you're pushing through matagouri or lawyer vine.
Taped seams: the part that actually decides it
This is the single biggest difference between a jacket that keeps you dry and one that doesn't, and it's the spec most often left off the label.
Every seam is a line of needle holes punched clean through your waterproof membrane. A jacket has hundreds of them per seam. It does not matter how good the fabric is - unsealed, those holes leak, and they leak first at the shoulders where your pack presses down.
Seam taping is a strip of waterproof tape heat-bonded over the stitch line on the inside. Two versions exist, and the distinction is worth money:
- Critically taped - only the seams most likely to get hit: shoulders, hood, upper chest. Cheaper. Leaks eventually, somewhere else.
- Fully taped - every seam sealed. What you want in a jacket you'll rely on.
If a product page states a big mm number but says nothing about seams, assume they're not taped. The Outlander is fully taped - every seam, not just the obvious ones.
DWR: why your jacket "leaks" when it hasn't
DWR stands for durable water repellent - a finish applied to the outer face of the fabric that makes rain bead up and roll off.
DWR isn't what makes a jacket waterproof. The membrane does that. What DWR does is stop the outer fabric from soaking up water in the first place, and that turns out to be critical, because of this:
When the DWR wears off, the face fabric absorbs water and goes dark and heavy. This is called wetting out. The membrane underneath is still perfectly waterproof - but a saturated face fabric can no longer let vapour escape. Your sweat has nowhere to go, it condenses inside, and you get wet and cold.
Almost every "my waterproof jacket is leaking" complaint is actually a dead DWR. The good news is it's fixable in an afternoon for about twenty dollars.
How to tell if your DWR has gone
Hold the jacket under a tap. If the water beads and runs off, it's fine. If it soaks in and the fabric darkens, the DWR is finished.
How to bring it back
- Wash it. Body oils, sweat, sunscreen and dirt kill DWR faster than wear does. Use a technical wash, not standard detergent - detergent leaves residue that attracts water.
- Heat it. Many DWR finishes reactivate with gentle heat. Tumble dry low for 20 minutes, or press with a warm iron and a cloth between. Check your care label first.
- Reproof if that fails. A wash-in or spray-on treatment. Spray-on is better for jackets with a liner, since it only treats the outer face.
A note on PFAS
DWR chemistry is changing fast. The finishes that performed best have historically been fluorocarbon-based - the PFAS family - and regulators are phasing them out. California and New York banned intentionally added PFAS in apparel from January 2025, with carve-outs for severe-weather outdoor gear that run to 2028. Maine, Vermont, Connecticut and France followed in January 2026, and EU restrictions on related compounds took effect in April 2026.
New Zealand has no equivalent apparel ban yet, but supply chains are global, so the shift is coming here regardless. The practical consequence for you: PFAS-free DWRs - polyurethane, silicone and wax-based - bead water well when new but are generally less wash-durable than what they replaced. Plan on reproofing more often than you used to. That's the trade, and it's a fair one.
The openings: zips, hood, cuffs, hem
You can get all of the above right and still get wet through a badly built opening.
- Zips - a plain zip is a water highway. Look for either a laminated waterproof zip or a proper storm flap covering it. Flaps are more common because waterproof zips are stiff, expensive and wear out.
- Hood - must adjust with one hand, because the other one is holding something. A hood that doesn't turn with your head funnels rain onto your face.
- Hem - a drop hem (longer at the back) is the difference between dry and soaked when you're bent over a fence strainer or crouched on a hill.
- Cuffs - adjustable, and tight enough to seal under a glove. Water running down your forearm is a common and very cold failure.
This is where cheap jackets get caught out, and it's the easiest section to check yourself in a shop. The Outlander ticks all four: a laminated waterproof zip rather than a storm flap - the more expensive way to do it, and the one that doesn't flap open in wind - plus one-handed hood adjustment, adjustable cuffs, and a drop hem for when you're bent over.
Waterproof vs water-resistant vs showerproof
| Term | What it actually means |
|---|---|
| Waterproof | Rated membrane or coating, sealed seams. Keeps water out under pressure, for hours. |
| Water-resistant | Tightly woven fabric, usually a DWR, no sealed seams. Handles a shower. Fails in sustained rain. |
| Showerproof | A marketing word with no test behind it. Treat as water-resistant. |
| "Weatherproof" | Also a marketing word. Ask for the mm rating. |
How to check a jacket before you buy it
- Is there an mm rating? No number means no test. Walk away.
- Is there a breathability figure? A waterproof number alone is half the story.
- Are the seams taped, and fully or critically? If it doesn't say, assume the worse one.
- What's covering the main zip? Storm flap or laminated zip, one or the other.
- Does the hood adjust one-handed and turn with your head? Put it on in the shop and look sideways.
- Is the back hem longer than the front?
- Can you get a mid-layer under it without the shoulders binding? A shell that only fits over a t-shirt is a summer jacket.
What you actually need for New Zealand
NZ rain has a particular character: it arrives with wind behind it, it doesn't pass quickly, and it finds you a long way from the car. Nor'west rain on the Canterbury foothills is not a shower to sit out - it's four hours of horizontal water at temperatures that drop as the day goes on.
For that, the honest answer for most people is 10,000mm waterproof, around 10,000g breathability, fully taped seams, a ripstop face fabric, and a hood that works. Above that you're buying capability for conditions you'll meet a handful of times, at a price that stops you buying the mid-layer that would have kept you warmer anyway.
That's exactly how we specced the Outlander Waterproof Jacket - $199.99, unisex fit, XS through 5XL. And because a shell only works as part of a system, it also anchors our layering bundle alongside the Headland Thermal and Huntaway Fleece - base, mid and shell for $259.99.
A waterproof jacket isn't the thing that keeps you warm. It's the thing that stops the weather taking your warmth away. Get the shell right and the rest of your layers can finally do their job.
Frequently asked questions
Is 10,000mm waterproof enough?
Yes, for almost everything most people do outdoors in New Zealand. 10,000mm handles sustained heavy rain, pack straps and kneeling on wet ground. Ratings above 20,000mm are aimed at extended alpine and expedition use, and the extra headroom is rarely called on.
What's the difference between waterproof and water-resistant?
Waterproof means a tested membrane or coating plus sealed seams, so water can't get through under pressure. Water-resistant means a tightly woven fabric with a repellent finish and no sealed seams - it sheds a passing shower and fails in sustained rain.
Why is my waterproof jacket leaking?
Usually it isn't. The most common cause is a worn-out DWR finish letting the outer fabric soak up water, which blocks breathability and causes your own sweat to condense inside. Wash the jacket with a technical wash, tumble dry on low to reactivate the finish, and reproof it if that doesn't work.
Does a higher mm rating always mean a better jacket?
No. A high waterproof rating paired with low breathability will leave you wet from the inside. Sealed seams, a working DWR and well-built openings affect whether you stay dry far more than the difference between 10,000mm and 20,000mm.
How long should a waterproof jacket last?
A well-made shell used regularly should give five to ten years. The DWR needs restoring every 10-20 washes or once a season under hard use. What eventually ends a jacket is delamination or abrasion damage, not the membrane wearing out.
Can you make an old jacket waterproof again?
You can restore the water-repellent finish with a wash-in or spray-on treatment, and that fixes the large majority of jackets people think have failed. What you can't repair at home is a delaminated membrane or seam tape that has lifted - at that point the jacket is finished as a shell.
What does ISO 811 measure?
ISO 811 is the international hydrostatic head test. Water pressure is increased against a clamped fabric sample at a fixed rate of 100mm per minute until three droplets appear on the far side. The pressure at that point, in millimetres of water column, is the fabric's waterproof rating.