Most ski jackets and pants list a waterproof rating such as 10K or 20K, and often a breathability rating too. The numbers look technical, but they are easy to read once you know what was measured. Here is what they mean and how to use them when you shop.
What the waterproof number measures
The waterproof rating is usually given in millimetres (mm). In a lab test, a column of water is placed on the fabric and the height is increased until water starts to come through. "10K" means the fabric held back a 10,000 mm column of water; "20K" means 20,000 mm. The higher the number, the more water pressure the fabric can resist.
Water pressure matters more than you might think. Kneeling in wet snow, sitting on a damp chairlift or wearing a backpack all press water into the fabric, which is why the seat and knees of snowboard pants take the most punishment.
A rough guide to waterproof ratings
- Up to 5K (water-resistant): handles light snow and short showers on dry, cold days. Good for layers and après-ski.
- 5K to 10K: suits dry snow and average resort days.
- 10K to 15K: a good all-round range for most resort riding, including some wet snow.
- 15K to 20K: better for wet snow, sleet and long days outside.
- 20K and above: for very wet conditions, storms and riders who spend a lot of time sitting or kneeling in the snow.
These ranges are a general guide used across the outdoor industry, not a strict standard. Test methods also vary between brands, so treat the number as a useful comparison rather than a guarantee.
What the breathability number means
Breathability is usually given in grams per square metre per 24 hours (g/m²/24h). It describes how much water vapour from sweat can pass out through the fabric in a day. A higher number means sweat escapes more easily, so you stay drier from the inside.
- Around 5K: fine for relaxed resort days.
- 10K to 15K: a good balance for most riders.
- 20K and above: helpful for very active riding, hiking and park laps.
Ratings are not the whole story
A high rating on the fabric only helps if the rest of the garment keeps water out too. Look for:
- Taped seams: stitching makes tiny holes, and seam tape seals them.
- Water-resistant zips or storm flaps over the main zips and pockets.
- A DWR finish on the face fabric, so water beads up instead of soaking in.
- Snow protection: a powder skirt on jackets and boot gaiters on pants keep snow out where water ratings cannot help.
Water-resistant vs waterproof
"Water-resistant" pieces shed light snow and drizzle, usually thanks to a tightly woven fabric and a DWR finish, but they are not built to stay dry in heavy, wet snow. "Waterproof" pieces use a membrane or coating and come with a rating, typically 10K or higher for ski wear.
Which rating do you need?
- Dry, cold mountains and short sessions: 10K is usually enough.
- Mixed conditions at the resort: 10K to 15K jackets and 15K or higher pants.
- Wet snow, coastal mountains or long days: 20K, especially for pants if you sit or kneel a lot.
- Layers and après-ski: a water-resistant hoodie or sweater is fine under or instead of a jacket on dry days.
Finding the ratings on Hellystudio products
Our range includes pieces rated 10K, 15K and 20K waterproof, plus a few water-resistant layers with a DWR finish. Where a product has a rating, you will find it under CORE FEATURES on the product page, often together with the breathability rating and details such as taped seams.
Shop this guide: Ski Jackets · Baggy Ski Pants · Snowboard Hoodies
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