Waterproof claims come in at least three different measurement systems, none of which are interchangeable, and a jacket can be genuinely waterproof and still let you get wet. Here is what each number means.
IP ratings: for electronics
The IP code has two digits. The first is protection against solids, the second against water.
| Code | Water protection |
|---|---|
| IPX4 | Splashing from any direction |
| IPX5 | Low-pressure jets |
| IPX6 | High-pressure jets |
| IPX7 | Immersion, 1m, 30 minutes |
| IPX8 | Immersion beyond 1m, as stated by the maker |
Two things people get wrong:
- An X means "not tested", not "failed". IPX7 and IP67 are identical for water.
- The scale is not cumulative at the top. IPX7 is immersion; IPX6 is jets. A device rated IPX7 has not necessarily passed the jet test, which is why you sometimes see IPX6/IPX8 quoted together.
Salt water, chlorine and sweat are outside the test, which uses fresh water. So is pressing buttons underwater.
Hydrostatic head: for fabric
Outdoor fabric is rated in millimetres — 5,000mm, 10,000mm, 20,000mm. It is the height of a column of water the fabric holds before it leaks.
Rough guide:
- 1,500mm — the legal minimum for "waterproof" in the UK and EU. Light showers only.
- 5,000mm — light rain, short exposure.
- 10,000mm — sustained rain. A sensible general outdoor standard.
- 20,000mm+ — heavy rain, wind-driven, or pressure from a pack's straps and from kneeling.
Pressure is the part people miss. Sitting down, kneeling, or a rucksack strap pressing on a shoulder all push water through a fabric that would have held it standing still. That is why a high figure is worth having even in moderate rain if you carry a pack.
Breathability, and why it decides comfort
A fabric that keeps all water out and lets no vapour through will leave you wet from the inside. Breathability is measured as MVTR — grams of water vapour passing a square metre in 24 hours.
- 5,000g — low. Fine for standing around.
- 10,000–15,000g — moderate. Walking.
- 20,000g+ — high. Running, cycling, anything uphill.
The two numbers are usually quoted together, as 10k/10k or 20k/20k. Buying a very waterproof jacket with poor breathability for active use is the most common way to be disappointed by an expensive coat.
The DWR finish, and why jackets "stop working"
Almost every waterproof jacket has a Durable Water Repellent coating on the outer face. It makes water bead and roll off.
DWR wears off — from abrasion, dirt, body oils and washing. When it goes, the outer fabric absorbs water instead of shedding it. The membrane underneath is still waterproof, but the wet outer layer blocks vapour from escaping, so you feel damp and conclude the jacket has failed.
It usually has not. Washing the jacket with a technical cleaner and reproofing it restores the behaviour. This is maintenance, not a defect, and most jackets need it every few months of regular use.
Water resistant, waterproof, and taped seams
"Water resistant" has no standard behind it. Treat it as "will survive a short shower".
"Waterproof" on clothing sold in the UK and EU implies at least 1,500mm hydrostatic head — which is a low bar.
The detail that separates a real waterproof from a nominal one is taped seams. Every stitch is a hole. Fully taped seams are sealed with heat-bonded tape on the inside; critically taped means only the shoulders and hood. An untaped "waterproof" jacket will leak at the shoulders first.
What to check before buying
- Hydrostatic head of at least 10,000mm if you will be out for hours.
- Breathability matched to how hard you will be working.
- Fully taped seams.
- A hood that adjusts and turns with your head.
- Whether the zips are water-resistant or storm-flapped — an untreated main zip is a long vertical leak.
More kit notes are filed under Outdoors & Travel.