Understanding a product's waterproof rating is crucial for ensuring it meets your needs, especially for outdoor gear like jackets, tents, and backpacks. The most common and industry-standard measurement for waterproofness is the hydrostatic head (HH), which is expressed in millimeters (mm).
Understanding Hydrostatic Head (HH)
The hydrostatic head (HH) is a standardized test that measures the maximum amount of water pressure a fabric can withstand before water begins to leak through. Imagine a column of water placed on top of the fabric; the height of this column, in millimeters, at which the fabric starts to leak, is its HH rating.
The higher the HH rating, the more waterproof the fabric or product is. This directly indicates its ability to resist water penetration under various conditions, from light drizzle to heavy downpours and sustained pressure.
What Different Ratings Mean in Practice
Here's a breakdown of common hydrostatic head ratings and what they generally signify for practical use:
| Hydrostatic Head (HH) | Practical Application & Weather Suitability |
|---|---|
| 0 - 1,500 mm | Water-resistant, not fully waterproof. Suitable for very light rain or mist for short periods. Offers minimal protection against sustained wetness. |
| 1,500 - 5,000 mm | Good for light to moderate rain. Ideal for everyday use, city commuting, or short outings where heavy rain is unlikely. Common for budget rain jackets. |
| 5,000 - 10,000 mm | Suitable for moderate to heavy rain. Good for general outdoor activities, hiking, and camping in changeable weather. Provides solid protection against typical wet conditions. |
| 10,000 - 20,000 mm | High performance for heavy rain and snow. Excellent for more demanding outdoor sports like skiing, snowboarding, or extended treks in persistent wet weather. Can withstand significant pressure. |
| 20,000 mm+ | Extreme waterproofing. Designed for very harsh conditions, prolonged exposure to heavy rain, or activities involving sitting on wet surfaces (e.g., mountaineering, extreme winter sports). |
Key Factors to Consider
Beyond the HH rating, other elements contribute to a product's overall waterproof performance:
- Seam Sealing: A fabric might be highly waterproof, but if the seams where pieces are stitched together are not taped or sealed, water can easily seep through these needle holes. Look for "fully taped seams" or "sealed seams."
- Durable Water Repellent (DWR) Coating: Many waterproof items feature an external DWR treatment. This causes water to bead up and roll off the surface, preventing the face fabric from becoming saturated and allowing the underlying waterproof membrane to work effectively. DWR coatings can wear off over time and may need reapplying.
- Design and Features: Elements like storm flaps over zippers, adjustable cuffs, and waterproof zippers all enhance a product's ability to keep water out.
- Breathability: While not directly a waterproof rating, breathability (often measured in MVTR - Moisture Vapor Transmission Rate) is a crucial partner to waterproofing. Highly waterproof fabrics can feel clammy if they don't allow internal moisture (sweat) to escape. Many high-performance waterproof materials offer a balance of both.
How to Choose the Right Waterproof Rating
To select the appropriate waterproof rating, consider these points:
- Activity Type:
- Casual use/City: 1,500 - 5,000 mm is often sufficient.
- Hiking/Camping: 5,000 - 10,000 mm provides a good balance.
- Skiing/Mountaineering/Extreme weather: 10,000 mm and above is recommended.
- Expected Weather Conditions:
- Light drizzle/Intermittent rain: Lower ratings might be acceptable.
- Heavy rain/Prolonged exposure: Opt for higher ratings.
- Duration of Exposure:
- Short periods: A lower rating might suffice if you're not out long.
- All-day exposure: Higher ratings are essential to prevent saturation and discomfort.
- Pressure Points: If you'll be sitting on wet ground (e.g., camping tent floor) or wearing a heavy backpack, the fabric will experience more localized pressure, requiring a higher HH rating to prevent leaks.
By understanding the hydrostatic head rating and considering these additional factors, you can confidently choose gear that will keep you dry and comfortable in any weather.
