What do Waterproof Ratings actually mean?

What do Waterproof Ratings actually mean?

British summers are never straight-forward, especially when it comes to predicting the weather. That is why you need outdoor kit that can protect you when the heavens open at a minute's notice. However, understanding what to buy can be difficult, as there are multitudes of different materials, features and fabrics that companies use to showcase their protective technologies. Waterproof ratings in outdoor gear refer to the level of protection that a product provides against water penetration. These ratings are typically expressed in millimetres and indicate how much water pressure a material can withstand before it begins to leak.

How is Waterproofing Measured?

The most common waterproof rating system for outdoor gear is the International Organization for Standardization (ISO) 811 standard. This standard rates materials based on their ability to withstand water pressure, with a higher number indicating a higher level of waterproofness. To measure how waterproof a fabric is, tent manufacturers use a method called the Hydrostatic Head (HH) test. HH is the term for a material’s water resistance. They clamp sample material onto the bottom of a clear graded tube, then slowly fill the tube with water, waiting for at least three drops of water to finally seep through. The height of the water in millimetres at the point of leaking becomes the fabric’s waterproof rating. 

Protective coatings are applied to tent fabrics which close the gaps between threads, preventing water passing through the fabric and allowing water to bead and run off and maintain the quality of the material. Typically these coatings are polyurethane (PU) for polyester fabrics and silicone (Sil) for nylon fabrics. The application process, thickness and number of applied coatings are used to achieve the desired HH. For example, a tent with a rating of 5,000 mm can withstand 5,000 millimetres of water pressure before it begins to leak.

Other factors, such as the design of the product and the quality of the construction, can affect how well it keeps you dry. Additionally, waterproof ratings only refer to the fabric's ability to repel water, and not to the seams or zippers, which can also allow water to penetrate. For this reason, it's important to look for products with sealed seams and waterproof zippers for maximum protection against the elements.

Factors to take into account

Here are a few more things to keep in mind when it comes to waterproof ratings in outdoor gear:

Breathability: While it's important for outdoor gear to be waterproof, it's equally important that it's breathable. Breathability refers to a material's ability to allow moisture (like sweat) to escape from inside the garment, preventing you from getting wet from the inside out. Look for products with both a high waterproof rating and a high breathability rating for the best performance in wet conditions.

Different gear, different waterproof ratings: For example, a tent may have a higher waterproof rating than a pair of hiking boots, since it's designed to protect you from heavy rain and standing water. Be sure to check the waterproof rating for each specific piece of gear you're considering.

Degradation: Even if a product has a high waterproof rating when it's new, that rating can degrade over time as the fabric becomes worn or damaged. Be sure to take proper care of your gear (like washing it according to the manufacturer's instructions and storing it properly) to help it last as long as possible.

Water-resistant or water-repellent: Products that are labelled as "water-resistant" or "water-repellent" are not the same as those that are labelled as "waterproof." Water-resistant and water-repellent materials can help keep you dry in light rain or drizzle, but they will not provide the same level of protection as waterproof materials.

Waterproofing Treatments

While it's not always necessary to use additional waterproofing treatments on already waterproof gear, it can be a good idea in some cases. Over time, the waterproofing on gear can degrade or wear off as mentioned, reducing its effectiveness. By using a product like Nikwax, you can restore the waterproofing properties of your gear and help it last longer. Additionally, some products may not be fully waterproof to begin with or may have areas that are more susceptible to water penetration, such as seams or zippers. In these cases, extra waterproofing can provide an added layer of protection against the elements. Overall, while not always necessary, using a product like Nikwax can help ensure that your gear performs at its best, keeping you dry and comfortable during all your outdoor adventures.


In conclusion, understanding waterproof ratings in outdoor gear is an important aspect of choosing the right gear for your needs. It's important to note that the rating system may not be standardized across all manufacturers. Additionally, breathability is just as important as waterproofing, and different types of outdoor equipment may have different waterproof ratings. It's also important to note that waterproof ratings can degrade over time and that water-resistant or water-repellent materials are not the same as waterproof materials. By taking these factors into consideration, you can make informed decisions about what outdoor gear will best protect you against the elements and keep you comfortable during your outdoor adventures. You may even end up as happy in the rain as this guy!