How Does My Waterproof Jacket Work?

By Alpkit

Brands use a lot of technical language when they talk about waterproofs, mostly because lot of tech goes into making your waterproof work!

There's a huge amount of jargon to get your head around. But knowing how breathable waterproof fabrics work can help you decide which one to buy as well as how to look after it and extend its life.

  1. How are waterproof fabrics constructed?
  2. How do you measure waterproofness?
  3. How is breathability measured?
  4. What are durable water repellents?

Waterproof Fabric Construction

Waterproof fabrics are made up from a sandwich of different layers, including a breathable waterproof membrane. This membrane blocks rain droplets but still allows sweat vapour to pass through, keeping you dry on the outside and on the inside. The number of layers tells you how your waterproof jacket is constructed and will give you an indication of its quality.


A diagram to show how 2 layer waterproof fabrics are constructed

2 Layer Fabrics

Made from a face fabric bonded to a waterproof membrane, often with a separate mesh or fabric lining sewn in for comfort and protection. 2 layer fabrics are the cheapest of the bunch, but the sewn-in lining usually makes them heavier and much less breathable.




A diagram to show how 2.5 layer waterproof fabrics are constructed

2.5 Layer Fabrics

These fabrics are similar to two layer fabrics but they have a protective print on the inside (that’s the half layer) to protect the membrane. Sometimes this print contains carbon or silica, which makes it feel more comfortable next to your skin. 2.5 layer fabrics usually very lightweight and highly packable.




A diagram to show how 3 layer waterproof fabrics are constructed

3 Layer Fabrics

These fabrics consist of a face fabric, waterproof membrane and backer fabric, all bonded together. They’re more expensive than 2 and 2.5 layer jackets but they usually have better performance. The backer fabric protects the waterproof membrane and stops it from sitting directly against your skin. As a result, they’re much more durable and comfortable to wear.

Face and backer fabrics vary hugely which can dramatically affect your jacket’s characteristics. The face fabric has the greatest effect on the jacket’s weight, feel and durability – it can be soft and flexible for moving fast or tough as nails for protection. The backer fabric has the biggest impact on next-to-skin comfort – we always look for something soft and moisture wicking . Our most important job as product designers is to choose the right fabrics for the jacket, depending on its end use.

Laminates and Coatings

The fabrics listed above (2, 2.5 and 3 layer) are like the ones above: a thin waterproof membrane bonded to the outer shell fabric. But some manufacturers make coated waterproof fabrics too. Coated fabrics are where a waterproof coating (usually Polyutherene) has been spread over the inside of the shell fabric. The main difference you'll notice between laminate and coated fabrics are breathability and price.

Coated fabrics are much less breathable – it isn't possible to make the coating as thin as you could make a membrane. Laminate fabrics perform better because we can make the waterproof membrane incredibly thin to maintain breathability. However, the cost of manufacturing laminate fabrics means you do pay more for them.

Waterproofing And Hydrostatic Head

The hydrostatic head (HH) rating tells you how much water pressure your jacket can handle before it lets water in. It’s measured using a column of water (10cm diameter for the fabric geeks out there). The value signifies the height of the column required for water to leak through. We recommend that you look for a minimum of 10,000mm HH for most activities, or at least 20,000 for proper all-weather use. Alpkit’s waterproofs range from 10,000 – 30,000mm).


A diagram to explain how hydrostatic head tests work for measuring how waterproof waterproof clothing is

Generally speaking, the more you use your jacket, the more rain it will need to endure, so the higher the hydrostatic head you’ll need. It's also worth saying that rucksack straps increase the water pressure on your waterproof as they push water through the fabric. If you’re often wearing a heavy rucksack, you may need a waterproof with a higher hydrostatic head.

Breathability And Moisture Vapour Transmission Rate

The most waterproof jacket in the world won’t be very comfortable if it's not breathable. The moisture you produce when exercising needs somewhere to escape to. If moisture can’t pass through your jacket fast enough, it will accumulate on the inside of the jacket and feel wet.

Breathable fabrics are fabrics that allow moisture to pass from inside the fabric to the outside. One measurement of breathability is Moisture Vapour Transmission Rate (MVTR), measured in grams per square metre per day (g/m²/24hrs). We recommend the following guidelines for MVTR:

  • 8,000 is suitable for sedentary activities

  • 10,000 – 15,000 is breathable enough for most activities where you’d expect to sweat a bit – e.g. hillwalking.

  • 20,000 is excellent for intense activities when you’ll really be pushing yourself.

A diagram of how fabrics with breathable waterproof membranes work

Don’t get hung up on the numbers

MVTR is a tricky measurement: there are multiple methods for testing it and each method favours different fabrics. Manufacturers usually just quote the most flattering results for their garments, which can make comparisons difficult.

What else could affect your waterproof’s breathability?

Humidity
Breathability in waterproof jackets depends on 'solid state diffusion': water vapour is absorbed through the fabric and passed to the other side. The water vapour will always try to move to the least humid side of the fabric to maintain an equilibrium. In most conditions this means the water passes from the inside to the outside of the jacket. However, when it’s very humid, your jacket will feel less breathable.

Air permeability
Air permeability is the measurement of how much air a fabric allows to pass through it. Not all waterproofs have an air permeability rating, but jackets with this rating will probably have a lower MVTR than jackets without. This doesn’t necessarily mean they’re not as breathable, as you’re less likely to overheat when you’ve got a bit of airflow in your jacket.

Features
Pockets in your jacket can affect the breathability because they add another layer of fabric to your jacket. Some jackets have crafty mesh pockets to reduce fabric and allow you to dump excess heat and sweat too.

Dirt and abrasion: Dirt and abrasion could be stopping your DWR from working, reducing breathability. Which brings us to...

What Are Durable Water Repellent Coatings?

A Durable Water Repellent (DWR) is a fabric coating that stops water from soaking into your jacket, causing it to bead up and roll off instead. Without a DWR coating, your jacket's outer fabric would ‘wet out’ (become saturated with water). When this happens your jacket loses its breathability, becomes heavier and feels colder because wet fabric conducts heat away from your skin. Regular cleaning and reproofing maintain the DWR coating so your jacket continues to repel water.

Water beading up into droplets on the surface of a waterproof fabric

Your DWR makes water bead up into droplets and roll off the surface of your waterproof so that it maintains its breathability

Durable water repellents and the environment

A manufacturer may tell you what type of DWR they use – C8, C6 or C0 – but this only really tells you how many carbon atoms the DWR has, and whether or not it contains PFCs. The only thing you really need to know about the DWR is what affect it has on the environment.

Historically, the outdoor industry exclusively used C8 DWRs for their incredible durability. You didn’t need to reproof your jacket much, but these chemicals were found to produce toxic by-products which linger in the environment for generations (PFOS and PFOA). As a result, the industry shifted to using C6 DWRs. These were less durable and required more maintenance than C8, but they didn't accumulate as much or produce toxic by-products.

However, all PFCs, even the less harmful C6 chemicals, build up in the environment. We don't yet know what damage PFCs may be causing so we've moved our entire waterproof range over to completely PFC-free C0 DWRs.

Water beading on the Alpkit Definition waterproof jacket, a 100% PFC-Free Mountaineering Waterproof

Gear That Costs Less And Works Harder

Hopefully, you should now have a better idea of what all that complicated spec on your waterproof jacket means. We take pride in designing products from the ground-up, tailoring fabrics, fit and features to the jacket’s end-use. You won’t find any unnecessarily expensive name brands like Gore-Tex® or eVent®  here.

To source our technical fabrics, we work directly with our own fabric mills, factories and suppliers. The fabric we used for our high performance mountaineering jacket, the Definition, is completely unique, developed especially for us. Our missions as designers to produce gear that costs less and works harder.

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