Jacket specifications can read like a foreign language. Numbers like "20,000mm hydrostatic head" and "15,000g/m²/24h MVTR" appear on hang tags and product descriptions, but what do they actually mean for keeping you dry and comfortable? This guide decodes waterproof and breathability ratings, helping you understand what you're paying for and what you actually need for Australian conditions.
Understanding these numbers matters because marketing terms like "waterproof" and "water-resistant" lack consistent definitions across the industry. The technical specifications tell the real story—once you know how to read them.
How Waterproofing is Measured
The industry standard for measuring waterproofness is the hydrostatic head test. This test measures how much water pressure a fabric can withstand before moisture pushes through.
The Hydrostatic Head Test
Picture a tube filled with water placed on top of fabric. As more water is added, the column exerts increasing pressure. The height of water (measured in millimetres) at which droplets first penetrate the fabric is its hydrostatic head rating. A 10,000mm rating means the fabric withstood a column of water 10 metres high before leaking.
This testing method provides a standardised comparison between fabrics, though real-world performance involves additional factors like seam construction, zipper quality, and garment design.
What the Numbers Mean in Practice
Different activities and conditions require different waterproof ratings. Here's a practical guide to what various ratings handle:
- Under 5,000mm: Water-resistant only. Handles light rain briefly but will wet through in sustained precipitation
- 5,000-10,000mm: Light to moderate rain. Suitable for urban use and light outdoor activities in mild conditions
- 10,000-15,000mm: Moderate to heavy rain. Handles most Australian conditions competently
- 15,000-20,000mm: Heavy, sustained rain. Suitable for serious outdoor activities and extended exposure
- 20,000mm and above: Extreme conditions. Mountaineering, heavy storms, prolonged exposure
When you kneel, sit, or wear a heavy backpack, you add pressure equivalent to thousands of millimetres of hydrostatic head. This is why higher ratings matter for active outdoor use even if the rain itself wouldn't overwhelm a lower-rated fabric.
Understanding Breathability
Waterproofing alone doesn't make a good jacket. If a fabric blocks water from entering, it typically blocks water vapour (sweat) from escaping too. This is where breathability becomes crucial.
How Breathability is Measured
Breathability is most commonly measured as Moisture Vapour Transmission Rate (MVTR), expressed in grams per square metre per 24 hours (g/m²/24h). This indicates how much water vapour can pass through the fabric in a day. Higher numbers mean better breathability.
Some manufacturers use Resistance to Evaporative Heat Transfer (RET) instead, measured on a scale where lower numbers indicate better breathability. RET below 6 is excellent, 6-12 is good, and above 12 indicates limited breathability.
Why Breathability Matters
During physical activity, your body produces significant moisture through perspiration. A non-breathable jacket traps this moisture inside, leaving you wet from your own sweat even if no rain penetrates. This "clammy" feeling is uncomfortable and, in cold conditions, can be genuinely dangerous as wet clothing accelerates heat loss.
For casual urban wear, modest breathability suffices because activity levels are low. For hiking, cycling, or any strenuous activity, prioritising breathability becomes essential.
A jacket with 10,000mm waterproofing and 15,000g/m²/24h breathability will often outperform one with 20,000mm waterproofing and 8,000g/m²/24h breathability in real-world active use. Balance matters more than maximising a single spec.
Premium Membrane Technologies
Several branded membrane technologies dominate the high-performance waterproof market. Understanding their differences helps evaluate premium price points.
GORE-TEX
The most recognised name in waterproof breathable fabrics, GORE-TEX offers several product lines. GORE-TEX Pro is their top tier, used in premium mountaineering shells. GORE-TEX Active prioritises breathability for high-output activities. Standard GORE-TEX provides excellent all-round performance. GORE-TEX Paclite offers lightweight, packable options with somewhat reduced durability.
GORE-TEX carries a premium price but offers proven performance and the backing of Gore's Guaranteed To Keep You Dry warranty.
eVent
eVent membranes use a different approach that often delivers superior breathability compared to equivalent GORE-TEX products. Many serious outdoor athletes prefer eVent for high-output activities where moisture management is paramount. Less mainstream recognition means eVent jackets can sometimes offer better value.
Proprietary Technologies
Many brands develop in-house membrane technologies. Patagonia's H2No, The North Face's Futurelight, and Arc'teryx's partnership with GORE-TEX are examples. Quality varies, but proprietary technologies often offer good performance at lower price points than GORE-TEX alternatives.
The Role of DWR
Durable Water Repellent (DWR) is a treatment applied to the outer fabric of waterproof jackets. While the membrane provides waterproofing, DWR causes water to bead and roll off rather than saturating the outer fabric.
Why DWR Matters
When the outer fabric becomes saturated (called "wetting out"), several problems occur. First, the jacket becomes heavier and feels cold. Second, moisture vapour struggles to escape through wet outer fabric, reducing effective breathability. Third, the visual appearance suggests the jacket is failing even though the membrane remains waterproof.
DWR prevents wetting out, maintaining both performance and appearance. However, DWR degrades over time through abrasion, dirt accumulation, and repeated washing.
Maintaining DWR
DWR can be restored through heat reactivation (tumble drying on medium heat after washing) or by applying fresh DWR treatments. Regular maintenance keeps your jacket performing optimally even as the original treatment degrades.
DWR treatments have environmental implications. Some older formulations used PFCs (perfluorinated compounds) now recognised as environmental pollutants. Modern PFC-free DWR treatments address these concerns, though some performance compromises may exist. Check product specifications if environmental impact matters to you.
Seam Construction and Zippers
A fabric's waterproof rating means nothing if water enters through seams or zippers. Construction details matter as much as membrane specifications.
Seam Taping
Stitching creates needle holes that compromise waterproofing. Quality waterproof jackets address this through seam taping—applying waterproof tape over all stitching on the garment's interior. "Fully taped seams" indicates complete coverage; "critically taped seams" indicates coverage only in high-exposure areas, representing a cost-saving measure that compromises full waterproofness.
Zipper Technology
Main zippers can admit water if not properly designed. Solutions include water-resistant zippers with laminated teeth, storm flaps (fabric covers over zippers), and aquaguard zippers that create a waterproof seal when closed. Premium jackets typically feature multiple approaches for maximum protection.
What Australians Actually Need
With technical understanding established, what specifications make sense for typical Australian use cases?
Urban Commuting and Light Use
For general urban wear, 10,000mm waterproofing with moderate breathability (10,000g/m²/24h) handles most conditions. You're unlikely to face sustained heavy rain without shelter access, and activity levels remain low. Mid-range jackets from quality brands serve well without premium prices.
Day Hiking and Outdoor Recreation
Outdoor activities benefit from 15,000mm+ waterproofing and prioritised breathability (12,000g/m²/24h minimum). Activity levels are higher, conditions less controllable, and time to shelter longer. Fully taped seams and quality zippers become more important.
Alpine and Serious Outdoor Use
Mountain conditions and extended backcountry trips warrant premium specifications: 20,000mm+ waterproofing, maximum breathability, fully taped seams, and trusted membrane technologies. The investment makes sense when conditions are serious and help is distant.
- Casual/urban: 10,000mm / 10,000g adequate; value brands acceptable
- Hiking/recreation: 15,000mm / 12,000g minimum; quality construction matters
- Alpine/serious: 20,000mm+ / 20,000g+; premium membranes and construction
Understanding these numbers empowers you to evaluate jacket specifications critically, matching technical capabilities to your actual needs rather than paying for performance you'll never use—or, worse, buying inadequate protection for your intended activities.