Understanding Waterproof Ratings in Outdoor Gear
Outdoor gear manufacturers throw around numbers like "20,000mm waterproof" and "15,000g breathability" — but what do these actually mean for your comfort on the trail?
Waterproof Rating (Hydrostatic Head)
What It Measures
A column of water is placed on the fabric. The height (in mm) at which water begins to penetrate through is the waterproof rating.
What the Numbers Mean
| Rating | Protection Level | Suitable For |
|---|---|---|
| 0–5,000mm | Water resistant | Light drizzle, no sustained rain |
| 5,000–10,000mm | Moderately waterproof | Light to moderate rain |
| 10,000–20,000mm | Waterproof | Sustained rain, wet snow |
| 20,000mm+ | Highly waterproof | Heavy rain, high pressure (pack straps, kneeling) |
Real-World Context
- Sitting on wet ground creates ~2,000mm of pressure
- Pack straps pressing on your shoulders create ~5,000–8,000mm of pressure
- Kneeling creates ~10,000mm+ of pressure
- This is why "waterproof" jackets can wet out at the shoulders under a heavy pack
Breathability Rating
MVTR (Moisture Vapor Transmission Rate)
Measured in grams of water vapor that can pass through 1 square meter of fabric in 24 hours.
| Rating | Breathability | Activity Level |
|---|---|---|
| 5,000–10,000g | Low | Light activity, cool weather |
| 10,000–15,000g | Moderate | Moderate hiking |
| 15,000–20,000g | High | Fast hiking, moderate output |
| 20,000g+ | Very high | Trail running, high output |
RET (Resistance to Evaporative Transfer)
An alternative measurement where lower numbers are MORE breathable:
- RET < 6: Extremely breathable
- RET 6–12: Very breathable
- RET 12–20: Moderately breathable
- RET > 20: Low breathability
Common Waterproof Technologies
Gore-Tex
- Industry standard waterproof-breathable membrane
- Multiple versions: Gore-Tex Active (most breathable), Gore-Tex Pro (most durable), Gore-Tex Paclite (lightest)
- Rated ~28,000mm waterproof, ~15,000–25,000g breathability
eVent / Gore-Tex Active
- Air-permeable membrane — breathes without needing heat or humidity differential
- Among the most breathable waterproof options
- Excellent for high-output activities
Pertex Shield
- Budget-friendly waterproof-breathable fabric
- ~20,000mm waterproof, ~10,000–15,000g breathability
- Found in many mid-range jackets
DWR (Durable Water Repellent)
- A surface treatment (not waterproofing) that causes water to bead and roll off
- All waterproof jackets have DWR over the face fabric
- Wears off over time — reapply with Nikwax TX.Direct or Grangers
- When DWR fails, the face fabric absorbs water (wets out), which blocks breathability even though the membrane underneath still works
For Tents
Tent fabrics need higher waterproof ratings because:
- Rain hits with more force on a horizontal surface
- You press against the fabric from inside
- Seams are stress points
| Tent Part | Minimum Rating |
|---|---|
| Fly | 1,500mm+ (typical: 2,000–3,000mm) |
| Floor | 3,000mm+ (typical: 5,000–10,000mm) |
The Bottom Line
For most hikers, a jacket rated 15,000–20,000mm waterproof and 15,000g+ breathability handles nearly all conditions. The real difference maker is fit, features (pit zips, hood design), and DWR maintenance — not chasing the highest spec numbers.
Recommended Gear
Based on this guide's topics, here are some top-rated products to consider:
- Marmot Birdhouse 3-Shelf Hanging Tent Organizer ($34.95, 119 g)
- MSR Blizzard Tent Stakes ($29.96, 20 g)
- MSR Carbon Core Tent Stakes ($48.95, 6 g)
- Big Agnes Copper Spur HV UL2 Backpacking Tent - Olive Green / 2 Person ($549.95, 1.2 kg)
- Snow Peak Aluminum Tarp Pole ($59.95, 1.0 kg)
- Patagonia Capilene Cool Daily Graphic Hoody for Men - Fitz Roy Tarpon: Wispy Green X-Dye / L ($49.98, 181 g)
- Patagonia Capilene Cool Daily Graphic Hoody for Men - Fitz Roy Tarpon: Wispy Green X-Dye / M ($49.98, 181 g)
- Patagonia Capilene Cool Daily Graphic Hoody for Men - Fitz Roy Tarpon: Wispy Green X-Dye / XL ($49.98, 181 g)