What do waterproof and breathability ratings actually mean?

Picture this: you're out hiking and get caught in a sudden downpour, but instead of getting drenched, your baselayers look like they've just come out of the dryer. That's the magic of waterproof gear! But what exactly does "waterproof" mean, and how can you avoid swimming in your own sweat? That's where breathability and hydrostatic head ratings come in. So without further ado, let's dive in and demystify these technical terms.

Waterproof Ratings

Hydrostatic head, or simply "HH", is an industry-standard waterproof rating. This test is measured in millimetres (mm) and indicates how much water pressure a fabric can withstand before it starts to leak. The higher the rating, the more waterproof the jacket. To test this, a small piece of fabric is put under a column of water. The amount of water in the column increases until the point that water begins to soak through the fabric. For example, a HH rating of 10K refers to "10,000mm", which means 10 metres worth of water was able to be placed on top of that fabric without it leaking.

Here's a breakdown of common waterproof ratings

• 5,000mm and below: When it comes to waterproofing, the threshold begins at around 3,000mm. However, jackets in the 5,000mm and less range will only provide protection against light showers and drizzles. But they're often lightweight and packable, which makes them perfect for carrying on-the-go as your just-in-case option.
• 10,000mm: Jackets falling within this range are a great entry-level option. While they offer a decent level of waterproofing, they might not withstand heavy downpours or prolonged exposure to wet conditions. If you're planning outdoor activities in dry or mildly damp conditions, these jackets should serve you well.
• 15,000mm: This range strikes a balance between resistance to the elements and affordability for most people. With jackets in this range, you can expect reliable protection from rain, snow, and wet environments without breaking the bank.
• 15,000mm and above: These are the cream of the crop, and offer top performance in wet conditions. However, remember it's not all about waterproof rating. Eg: a 15K rain jacket with a high breathability rating will be more comfortable to wear than a heavy and unbreathable 20K jacket.

Breathability Ratings

Breathability is equally important to keep you comfortable during physical activities, as it allows moisture and sweat to escape from inside the jacket. A jacket with a high breathability rating won’t stop you from sweating — but what it will do is make it so that the water vapour that your skin releases can pass through the fabric and be released, rather than get stuck and pool together.

Breathability is measured in grams (g) and is represented as the jacket's Moisture Vapor Transmission Rate (MVTR). This is the amount of moisture that can pass through a square metre of fabric over the course of 24 hours. To measure breathability, fabric samples are placed in a controlled environment where the humidity and temperature levels are regulated. Moisture vapour is generated underneath the fabric, simulating the sweating process. The amount of moisture vapour that passes through the fabric over 24 hours is then measured and converted into the breathability rating. Here's what to look for:

• 0 g/m²/24hr: Jackets with minimal or no breathability may trap moisture inside, causing you to feel clammy and uncomfortable during strenuous activities. They are best suited for light use or as last-resort rain protection.
• 5,000 g/m²/24hr - 10,000 g/m²/24hr: Jackets in this range offer moderate breathability, allowing some moisture to escape while keeping you reasonably comfortable during low-intensity activities, like exploring cities during travel, or walking the dog.
• 10,000 g/m²/24hr - 15,000 g/m²/24hr: These jackets provide good breathability, allowing a significant amount of moisture to escape during active pursuits. They are suitable for hiking, commuting on your bike, or other moderate-intensity activities.
• 15,000 g/m²/24hr and above: Jackets with high breathability ratings excel in moisture management, efficiently venting sweat and heat. They are ideal for intense activities like trail running, cycling, or mountaineering, where you need optimal airflow to stay comfortable.

The importance of a good baselayer

There's no point dropping a fortune on the world's most breathable and waterproof jacket, if you're not wearing appropriate clothing underneath it. The job of a baselayer is to regulate your temperature by wicking moisture away. The saying "cotton kills" refers to the fact that cotton holds onto moisture which means that it will become heavy and cold when wet. Whereas polyester or merino wool allows moisture to pass through it, instead of absorbing it.

Other factors to consider

Remember, waterproof and breathability ratings work hand in hand to provide you with the best protection and comfort. Choosing a rain jacket that suits your specific needs and the activities you'll be engaging in is important. Keep in mind that these ratings are just one aspect of a rain jacket's overall performance. Other factors, such as seam sealing, fabric lining, hood design, and ventilation features such as pit zips, also play a role in determining the jacket's effectiveness in keeping you dry.

To conclude, understanding rain jacket ratings empowers you to make an informed choice. So, whether you're walking the dog or embarking on an epic outdoor adventure, the right rain jacket will help you stay dry, stay comfortable, and enjoy your time outdoors!