the-truth-about-tent-waterproof-ratings

CampDeck is reader-supported. When you buy through links on our site, we may earn an affiliate commission.

The tent waterproof rating, often expressed as mm HH (millimeters hydrostatic head), is a crucial factor in determining how well a tent will protect you from rain. But what does that number actually mean in real-world conditions? Many campers are confused by these ratings, and manufacturers sometimes play fast and loose with them. This article breaks down the science behind tent waterproof ratings, explains how they’re measured, and helps you understand how to choose a tent that will keep you dry on your next camping trip.

Understanding Hydrostatic Head (mm HH)

Hydrostatic head is a measure of how much water pressure a fabric can withstand before it starts to leak. It’s determined by placing a long tube over a piece of fabric and gradually filling it with water. The “head” refers to the height of the water column, and the mm HH rating is the height (in millimeters) at which water begins to penetrate the fabric.

The Testing Process

The test itself is relatively straightforward. A fabric sample is clamped under a sealed tube. Water is slowly added to the tube, increasing the pressure on the fabric. The height of the water column when the third drop of water penetrates the fabric is recorded as the hydrostatic head rating.

It’s important to note that different testing standards exist. The most common is the ISO 811 standard. However, some manufacturers may use slightly different methods, so it’s always best to look for independent verification of a tent’s waterproofness whenever possible.

What’s a “Good” Tent Waterproof Rating?

While there’s no universally agreed-upon definition, here’s a general guideline:

• 1,000mm - 1,500mm: Minimal protection. Suitable for light rain or condensation, but not recommended for prolonged or heavy downpours. Often found in budget tents or the inner tent of a double-wall tent.
• 1,500mm - 3,000mm: Moderate protection. Good for most camping conditions, including moderate rain. This is a common rating for many mid-range tents.
• 3,000mm - 5,000mm: High protection. Suitable for heavy rain and prolonged exposure. This is the minimum rating we recommend for serious backpacking or camping in areas with unpredictable weather.
• 5,000mm +: Excellent protection. Provides the highest level of waterproofness. Often found in expedition-grade tents designed for extreme conditions.

It’s worth noting that the floor of a tent usually has a higher HH rating than the body of the tent, as it bears more pressure from ground moisture and campers moving around inside. Floors often range from 3,000mm to 10,000mm.

Beyond the Numbers: Real-World Performance

While the mm HH rating provides a useful benchmark, it doesn’t tell the whole story. Several other factors influence a tent’s ability to keep you dry in the field.

Fabric Type and Coatings

The type of fabric used, and the coatings applied to it, significantly impact waterproofness and durability.

• Polyester: A common and relatively inexpensive option. Polyester is naturally water-resistant and holds up well to UV exposure. It’s often coated with polyurethane (PU) or silicone for added waterproofness.
• Nylon: Lighter and stronger than polyester, but also more expensive. Nylon is less naturally water-resistant and more susceptible to UV degradation. It’s typically coated with PU, silicone, or a combination of both.
• PU (Polyurethane) Coatings: These coatings are affordable and provide good waterproofness. However, they can be prone to hydrolysis (breaking down from moisture) over time, leading to a sticky or flaky texture.
• Silicone Coatings (SilNylon or SilPoly): Silicone coatings are more durable and UV-resistant than PU. They also add significant strength to the fabric. However, seams on silicone-coated fabrics cannot be taped, so they need to be sealed with a liquid seam sealant.

Seam Sealing: The Vulnerable Point

Even with waterproof fabric, a tent will leak if the seams are not properly sealed. Needle holes created during the sewing process compromise the waterproof barrier.

• Taped Seams: A waterproof tape is applied to the seams using heat and pressure, creating a watertight seal. This is the most common and effective method for PU-coated fabrics.
• Liquid Seam Sealer: A liquid sealant is brushed onto the seams, filling the needle holes. This is typically used for silicone-coated fabrics, as tape doesn’t adhere well to silicone. It requires more care in application than taped seams, but can be very effective.

Pay close attention to seam sealing when choosing a tent. Check for any gaps or imperfections in the tape or sealant. Re-sealing seams every few years is a good maintenance practice for extending the life of your tent.

Design and Construction

A well-designed tent will shed water more effectively than a poorly designed one. Features to look for include:

• Full Coverage Fly: A rainfly that extends all the way to the ground provides maximum protection from rain and wind.
• Bathtub Floor: A floor that curves up the sides of the tent creates a waterproof barrier against ground moisture and splashes.
• Proper Tensioning: A tent that is properly pitched and tensioned will shed water more effectively and prevent sagging, which can lead to leaks.

Maintaining Waterproofness

Even the best tent will lose some of its waterproofness over time due to wear and tear, UV exposure, and dirt accumulation. Regular maintenance can help extend the life of your tent and keep you dry.

Cleaning and Storage

• Clean Regularly: Dirt and grime can damage the fabric and coatings, reducing waterproofness. Clean your tent after each trip with a mild soap and water solution.
• Dry Thoroughly: Always make sure your tent is completely dry before storing it. Moisture can lead to mold and mildew growth, which can damage the fabric and coatings.
• Store Loosely: Avoid tightly packing your tent for long periods, as this can stress the fabric and coatings. Store it in a loose, breathable bag in a cool, dry place.

Re-Waterproofing

Over time, the waterproof coatings on your tent may degrade. You can restore waterproofness by applying a durable water repellent (DWR) treatment.

• DWR Sprays: These sprays can be applied to the exterior of the tent to add a water-repellent layer.
• Seam Sealer: As mentioned earlier, re-seal seams every few years to maintain a watertight seal.

Consider browsing our selection of backpacking tents to find a model that fits your needs. Also check our article on how to compare tents before you buy for more tips on selecting the right tent for your camping style.

Conclusion

Understanding tent waterproof ratings is essential for choosing a tent that will keep you dry and comfortable on your camping trips. While the mm HH rating provides a useful benchmark, it’s important to consider other factors such as fabric type, seam sealing, and design. By taking these factors into account and performing regular maintenance, you can ensure that your tent will perform well in all types of weather.