Jacket marketing loves numbers — 20,000mm waterproof, 800 fill power, three-layer construction. Most of them are real measurements, but they only tell you something once you know what they measure and which ones matter for what you’re actually doing.
A 20,000mm rating means nothing if the seams aren’t taped. An 800 fill power down jacket is superb until it rains.
This guide covers what the specifications actually mean, how to choose between insulation types, and what construction details separate a jacket that lasts from one that doesn’t. It’s part of our wider apparel and clothing section.
Waterproofing: What the Numbers Mean
Waterproof rating (mm) comes from a hydrostatic head test — how tall a column of water the fabric can hold back before it starts to leak.
| Rating | Handles |
|---|---|
| 0–5,000mm | Light rain, short exposure |
| 5,000–10,000mm | Moderate rain |
| 10,000–15,000mm | Sustained rain |
| 15,000–20,000mm | Heavy rain, real weather |
| 20,000mm+ | Storm conditions |
For genuine winter storms, most experts suggest 15,000mm or higher.
Breathability rating (g/m²/24h) measures how much moisture vapour escapes from inside. Higher is better. A useful range is 5,000 to 20,000 g/m²/24h — the top of that range is what you want if you’ll be working hard in the jacket.
Some manufacturers use RET instead (resistance to evaporative transfer), where lower is better. Under 6 is very breathable; under 13 is adequate.
Notably, Gore-Tex generally doesn’t publish breathability figures at all, though their fabrics typically test at 20,000+.
Seam Taping Matters More Than the Rating
This is the detail people miss. A fabric rated 20,000mm still leaks through the stitch holes if the seams aren’t sealed.
- Fully taped — every seam sealed. Necessary for serious weather.
- Critically taped — only the main seams (shoulders, hood). Adequate for light use, not for storms.
- Untaped — water-resistant at best, whatever the fabric rating says.
Judge a rain jacket on seam sealing and hood design before you judge it on the millimetre number.
DWR Is Not Waterproofing
Durable water repellent is a surface treatment that makes water bead up and roll off. It’s not what makes a jacket waterproof — the membrane does that.
DWR wears off with use and washing. When a jacket starts “wetting out” (the face fabric absorbing water and looking soaked), that’s DWR failure, not membrane failure. Reproofing sprays and wash-in treatments restore it, and this is normal maintenance rather than a fault.
Shell Construction
2-layer — membrane bonded to face fabric, with a separate hanging liner. Cheaper, heavier, comfortable. 2.5-layer — membrane with a printed protective coating instead of a liner. Lightest and most packable; can feel clammy. 3-layer — face fabric, membrane and backer all bonded together. Most durable and breathable, most expensive.
Insulation
Down
Down is the plumage under bird feathers, and it has the best warmth-to-weight ratio available.
Fill power measures loft quality — how many cubic inches one ounce of down occupies. Higher means more warmth per gram, not more warmth overall.
- 550–650 — budget to midrange; warm but heavier for the warmth
- 650–800 — the quality range for most jackets
- 800–900 — premium, excellent warmth-to-weight
- 900–1000 — specialist ultralight
Fill weight — how much down is actually in the jacket — matters just as much. A 900-fill jacket with very little down is a light layer; a 650-fill jacket packed generously is a genuinely warm coat. Fill power without fill weight tells you only half the story.
Typical down jackets run roughly 7 to 30 ounces total weight, with most sitting around 15 to 23 ounces.
Down’s weakness is water. Once it takes on significant moisture it clumps, collapses, and stops insulating. DWR finishes and hydrophobic down treatments help with light rain, but in sustained wet weather down is the wrong choice. Brands market water-resistant down heavily; be sceptical of how far that goes.
Look for RDS (Responsible Down Standard) or similar certification if ethical sourcing matters to you.
Synthetic
Synthetic insulation is polyester fibre engineered to mimic down’s structure.
It’s heavier and bulkier than down for the same warmth, and it doesn’t compress as small. What it does better is keep insulating when wet, dry faster, cost less, and avoid animal products entirely.
For consistently wet climates, synthetic is generally the better call — a point most gear testers make repeatedly about places like the Pacific Northwest.
Hybrid
Many current jackets combine both — down in the core where it stays dry, synthetic at the shoulders, cuffs and hood where moisture collects. A sensible design that plays to each material’s strengths.
Baffle Construction
Baffles are the chambers holding insulation in place.
Sewn-through — stitching passes straight through, creating cold spots along every seam line. Lighter and cheaper. Box baffle — fabric walls between layers, no stitch penetration, no cold spots. Warmer, heavier, pricier. Welded — bonded rather than stitched, eliminating needle holes. Good in wet conditions.
Jacket Types
Hardshell — waterproof and windproof, no insulation. A weather barrier to layer over. Softshell — stretchy, breathable, water-resistant but not waterproof. Excellent for active use in dry cold. Insulated jacket / puffer — down or synthetic fill, usually with a light shell. 3-in-1 — a shell and a zip-in liner that work separately or together. Versatile, though each layer is usually compromised versus a dedicated piece. Parka — longer cut, heavily insulated, for cold urban conditions. Fleece — knit pile, warm and breathable, but no wind or water resistance. Field and utility jackets — waxed cotton or canvas, durable and classic, water-resistant rather than waterproof. Leather — durable and wind-resistant, needs conditioning, no insulation on its own.
Construction Details
Two-way zips on longer coats — lets you open the hem for sitting or movement. Storm flap over the main zip, since zips are the most common leak point. Adjustable hood with brim, and preferably adjustable in three directions rather than one. Pit zips for dumping heat without removing the jacket. Adjustable cuffs and hem to seal out draughts. Pocket placement that stays usable while wearing a rucksack or a seatbelt — surprisingly often overlooked. Lining that moves freely rather than binding at the shoulders.
Choosing for Your Conditions
Wet and mild — waterproof shell with a high breathability rating, fully taped, plus synthetic insulation if you need warmth.
Cold and dry — down wins decisively. High fill power, generous fill weight, box baffles if warmth is the priority.
Cold and wet — synthetic or hybrid, with a waterproof shell.
Active use — prioritise breathability and pit zips over absolute warmth. You generate significant heat moving; over-insulating leads to sweat, and sweat leads to cold.
Urban commuting — a parka or insulated coat with a longer cut. Extreme technical ratings aren’t necessary.
Care
Wash technical jackets more often than you’d think. Body oils and dirt clog membranes and degrade breathability. Use a technical wash (not standard detergent, which leaves residues).
Reproof DWR when water stops beading. Wash-in or spray-on, then heat-activate in a dryer on low or with an iron on low with a cloth — check the label first.
Tumble dry down jackets on low with dryer balls. This is one of the few garments where the dryer helps — it breaks up clumps and restores loft. Air drying alone leaves down matted.
Store down uncompressed. Long-term compression permanently damages loft. Hang it or keep it loose rather than stuffed in its sack.
Wax or condition waxed cotton and leather periodically.
Common Problems
Jacket leaks despite a high rating. Almost always seams. Check whether it’s fully taped or only critically taped, and inspect for lifting tape.
Face fabric soaks through and feels clammy. DWR has worn off — the membrane is probably fine. Reproof it.
Down jacket lost its puff. Either clumping from washing (fix with a low tumble dry and dryer balls) or damage from long compression (not reversible).
Cold spots along the stitch lines. Sewn-through baffle construction. Inherent to the design, not a defect.
Sweating inside a waterproof jacket. Breathability limit reached, or all vents closed. Open pit zips; consider a more breathable membrane for active use.
Zip fails. The most common failure point on any jacket. Keep it clean and lubricated; a good repair shop can replace it for far less than a new jacket.
Down leaking through the fabric. Some feather escape is normal. Heavy loss means the shell fabric is too loosely woven or damaged. Pull escaping feathers back through from the inside rather than plucking them out.
Where to Go From Here
- Apparel & Clothing — garment construction and sizing fundamentals
- Pants & Bottoms — fit measurements and fabrics
- T-Shirts — base layers and fabric weight
- Fabric Types & Specs — membranes, face fabrics and construction
Related areas:
- Garment Manufacturing & QC — how seam sealing and construction quality are controlled
- Fabric Printing — decorating technical fabrics, which has its own constraints
Frequently Asked Questions
What waterproof rating do I actually need? For everyday rain, 10,000mm is adequate. For sustained heavy rain or winter storms, look for 15,000mm or higher. But the rating matters less than seam taping — an untaped 20,000mm jacket will leak at the stitch lines while a fully taped 10,000mm jacket won’t.
What is fill power, and is higher always better? Fill power measures down loft quality — warmth per unit weight. Higher means lighter for the same warmth, not warmer overall. A 650-fill jacket with plenty of down can be warmer than an 850-fill jacket with very little. Check fill weight alongside fill power.
Down or synthetic? Down for cold dry conditions — better warmth-to-weight and packability. Synthetic for wet conditions — it keeps insulating when damp and dries faster. In consistently wet climates, synthetic is usually the better choice despite down’s advantages on paper.
Can I wear a down jacket in the rain? Light rain briefly, yes, especially with a DWR finish and hydrophobic down. Sustained rain, no — down clumps when wet and loses its insulating ability. Brands promote water-resistant down heavily, but it has real limits. Wear a shell over it, or use synthetic.
My waterproof jacket stopped beading water. Is it broken? No — the DWR finish has worn off, which is normal. The membrane underneath is probably still fine. Wash it with a technical cleaner and reproof it; performance usually returns.
Why do I get wet inside my waterproof jacket? Usually condensation rather than leakage. If you’re generating more sweat than the membrane can transmit, moisture condenses inside. Open pit zips and vents, and look for a higher breathability rating if you’re active in it.
Should I tumble dry my down jacket? Yes — this is the exception. Washing clumps down together, and a low-heat tumble dry with dryer balls breaks up the clumps and restores loft. Air drying alone leaves the down matted and the jacket noticeably less warm.
What’s the difference between a hardshell and a softshell? A hardshell is fully waterproof and windproof with no stretch, designed as a weather barrier. A softshell is stretchy and breathable, wind-resistant and water-resistant but not waterproof, designed for active use in dry or lightly wet conditions. They solve different problems.
