Buying Guides
Waterproof Ratings Explained: What 10,000 mm Actually Means
"Waterproof 10K/10K" is the most quoted and least understood line on any jacket tag. Here's what the numbers measure, what they miss, and what to actually buy.
The waterproof number: hydrostatic head
The first number is the height of a water column, in millimetres, the fabric withstands before leaking under lab pressure.
| Rating | Handles | Honest label |
|---|---|---|
| < 5,000 mm | Drizzle, dry snow | Water-resistant |
| 5,000–10,000 mm | Steady rain, average winter | Waterproof (everyday) |
| 10,000–20,000 mm | Heavy rain, wet snow, wind | Waterproof (serious) |
| 20,000+ mm | Storms, pack straps, kneeling in slush | Expedition-grade |
Why you need more than "rain pressure": pressure spikes. Kneeling, sitting, pack straps and wind-driven rain push water through fabric far harder than falling drops. That's why 5,000 mm keeps you dry on a walk but soaks through where your backpack sits. For anything beyond city use, 10,000 mm is the sensible floor.
The breathability number
The second number (e.g. 10,000 g/m²/24h, "MVTR") measures how much water vapour escapes per day. Higher = less clammy during effort.
- 5,000 g: commuting, low output
- 10,000–15,000 g: hiking, resort skiing
- 20,000+ g: touring, winter running, anything sweaty
Caveat: test methods vary between brands, so cross-brand comparisons are approximate. Within one brand, the tiers are meaningful.
Layers: 2L, 2.5L, 3L
Membrane construction affects durability and feel more than raw numbers:
- 2L — membrane bonded to the face fabric, loose liner inside. Quieter, cheaper, bulkier. Fine for daily and resort use.
- 2.5L — printed protective layer instead of a liner. Lightest and cheapest to make; clammier against skin. Good packable emergency shells.
- 3L — membrane sandwiched between face fabric and inner scrim. Most durable, best next-to-skin feel, priciest. The choice for hard, frequent use.
The part everyone forgets: DWR
The membrane keeps water out, but the DWR coating on the face fabric keeps the fabric itself from soaking up water ("wetting out"). A wetted-out shell stops breathing entirely — you get wet from your own sweat and swear the jacket "leaks". It doesn't; its DWR died.
DWR wears off with use and washing. When water stops beading: wash the shell, re-apply DWR (spray or wash-in), tumble low to cure. This €15 ritual restores jackets people were about to replace.
Seams and zips
A membrane with unsealed seams is a colander. Look for fully taped seams (not "critically taped" if you'll be out in real weather) and water-resistant zips or storm flaps. This is also why the "waterproof" softshell with no taped seams is a marketing category, not a weather one.
The quick answer
City winter: 5–10K, 2L, and keep the DWR alive. Outdoors in real weather: 10–20K/10–15K, 3L, fully taped. And whatever you buy, the maintenance is the same: clean shell, fresh DWR, dry it fully.