Key takeaways
- A waterproof rating measures resistance to water penetration, usually as 'hydrostatic head' in mm.
- Higher mm means more waterproof: ~1,500mm is the entry 'waterproof' threshold; 10,000–20,000mm+ is robust.
- It lets you compare fabrics, but isn't the whole story — seams, construction, and DWR matter too.
- Breathability is rated separately, so a high waterproof number doesn't indicate breathability.
What a waterproof rating is
A waterproof rating measures how well a fabric resists water penetration, most commonly expressed as ‘hydrostatic head’ in millimeters (mm) — the height of a column of water the fabric can withstand before it leaks. The higher the number, the more waterproof the fabric.
What the numbers mean
- ~1,500mm — the entry threshold to be called ‘waterproof’.
- 5,000–10,000mm — handles moderate rain.
- 10,000–20,000mm+ — robust, durable waterproofing for sustained rain, snow, and pressure (pack straps, kneeling).
Comparing two rain jackets, a buyer sees one rated 10,000mm and another 20,000mm — and chooses the higher rating for a trip with sustained rain and a heavy pack, knowing it’ll better resist water being pressed through under the shoulder straps.
The rating isn’t everything
A waterproof rating is a useful comparison number, but real-world performance also depends on sealed seams, the garment’s construction, and a maintained DWR finish on the face fabric. And it’s separate from breathability — a high waterproof number says nothing about how breathable a membrane like Gore-Tex is.
The bottom line
A waterproof rating — usually hydrostatic head in mm — tells you how much water pressure a fabric resists before leaking, with ~1,500mm the 'waterproof' entry point and 10,000–20,000mm+ for serious conditions. It's a useful comparison number, but not the whole story: sealed seams, construction, and a maintained DWR matter too, and breathability is rated separately.
Frequently asked questions
What is a waterproof rating?
A waterproof rating measures how well a fabric resists water passing through it, most often given as 'hydrostatic head' in millimeters (mm). It represents the height of a column of water the fabric can hold back before water starts to penetrate. The higher the mm number, the more waterproof the fabric.
What waterproof rating do I need?
As a rough guide, around 1,500mm is often considered the minimum to call a fabric 'waterproof,' 5,000–10,000mm handles moderate rain, and 10,000–20,000mm or higher provides robust, durable waterproofing for sustained rain, snow, and demanding conditions or where pressure is applied (like under pack straps or when kneeling). Higher is more waterproof and tends to stay waterproof longer under stress.
Does a high waterproof rating mean the gear is high quality?
Not on its own. The rating reflects the fabric's resistance to water pressure, but real-world waterproofing also depends on sealed seams, the garment's construction, and a maintained DWR finish on the face fabric. Also, waterproofness and breathability are rated separately — a high waterproof number tells you nothing about how breathable the fabric is.
Sources
- Waterproof-breathable fabrics — The Mountaineers
- Fabric testing — Textile Exchange