Spotlight - equipment views and reviews from the AK team
How Does My Waterproof Jacket Work?
21, Dec, 2018
Understanding the technical jargon and specifications we use to describe your waterproof garments
Brands use a lot of tech language when they talk about waterproofs because lot of tech goes into making your waterproof work.
This post should give you an understanding of what all that jargon is telling you and how to you can use it to decide which waterproof jacket to buy.
Waterproof Fabric Construction
To understand how a waterproof jacket works you need to understand the various layers they can be made up of. The quantity of layers informs us about construction the fabric that your waterproof jacket is made of.
2 Layer Fabrics
Made of a face fabric and waterproof membrane, often with a mesh or fabric lining sewn in for comfort. 2 layer fabrics are the cheapest of the bunch, but the sewn in lining usually makes them much less breathable.
2.5 Layer Fabrics
Here you’ve got a face fabric, waterproof membrane and a 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.
3 Layer Fabrics
These have a face fabric, waterproof membrane and backer fabric on the inside. They’re more expensive than 2 and 2.5 layer jackets and they often perform better. Backer fabrics protect the waterproof membrane and prevent it from sitting directly against your skin, so they’re much more durable and comfortable to wear.
Face and backer fabrics vary and can affect your jacket’s characteristics. Backer fabrics often affect next-to-skin comfort (I look for something soft and moisture wicking – we want our garments to be a joy to wear!). The face fabric has the greatest effect on the jacket’s weight, feel and durability: can be soft and quiet for stealth or tough as nails for protection. Our job as designers is to select the right fabric for the garment, depending on its end use.
Laminates and coatings
Laminate fabrics are like the ones above: with a thin waterproof membrane bonded to the shell fabric. Some manufacturers make coated waterproof fabrics too, which means 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.
Laminate fabrics perform better because we can make the waterproof membrane incredibly thin to maintain breathability but the cost of the process of making these fabrics means you pay more for them.
Coated fabrics are less breathable: it isn't possible to make the coating as thin as you could make a membrane but they're also a lot cheaper.
The hydrostatic head 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 fact fans out there). The value signifies the height of the column required for water to leak through. I’d look for a minimum of 10k HH for most activities, or at least 20k for heavier use. Alpkit’s waterproofs range from 10,000 – 30,000 mm).
Generally speaking, the more you’ll be using your jacket and the more rain it will endure, the higher the hydrostatic head you’ll need. That said, rucksack straps put more pressure on your waterproof as they push water through the fabric, so if you’re wearing a heavy rucksack you’ll want a higher hydrostatic head too.
Moisture Vapour Transmission Rate
A super waterproof jacket won’t be comfortable to wear if it’s not breathable. The moisture you produce when exercising needs somewhere to escape to. If it can’t pass through your jacket (or breathe) fast enough, it will accumulate on the inside of the jacket and feel wet.
One measurement of breathability is Moisture Vapour Transmission Rate (MVTR), measured in grams per square metre per day. I’d 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, say hillwalking.
20,000 is excellent for intense activities when you’ll really be pushing yourself.
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 comparing difficult.
What else could affect your waterproof’s breathability?
Breathability in waterproof jackets depends on solid state diffusion, so 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, so 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.
Pockets in your jacket can affect the breathability because they add another layer of fabric to your jacket. Some jackets have crafty mesh pockets that let you dump a little heat too.
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.
Dirt and abrasion:
Dirt and abrasion could be stopping your DWR from working, reducing breathability. Read on for more on that one…
Durable Water Repellent Coatings
Durable Water Repellent (DWR) is a coating that stops water from sitting on your jacket, making it bead up and roll off instead. Without a DWR coating, the outer fabric would ‘wet out’ (become saturated with water), so your jacket would feel less breathable and heavier and you’d feel colder because the water in the fabric would conduct heat away from your skin. Regular cleaning and reproofing will maintain the DWR coating so your jacket continues to repel water.
Your DWR makes water bead up into droplets and roll off the surface of you waterproof so that it maintains its breathability
Environmental considerations: types of DWR
A manufacturer may tell you what type of DWR they use, for example ‘C6’ or ‘C8’. This actually tells you how many carbon atoms the DWR has, but what you need to know is the effect that this has on the environment. Historically, C8 DWR was used on waterproofs for its incredible durability. You didn’t need to reproof it much, but it produced toxic by-products which linger in the environment for generations. So we now use C6 DWR, which is less durable and requires more maintenance that C8, but poses less of a threat to the environment.
Product designer Ronnie wrote a techy Spotlight post on why you need to reproof your waterproof, read what she has to say here. If you want to get down to business and just reproof it, head over to our reproofing your waterproof step-by-step instructions instead.
We hope this has given you a better idea of what all the spec means on your waterproof jacket. We take pride in designing products from the ground-up, tailoring everything from fabrics to features to the jacket’s end-use. We work directly with our factories and suppliers, you won’t find any name brands here, to source our technical fabrics. In brief, we know our stuff, so if you want any more information about the spec of our waterproof jackets, feel free to get in touch with our support team!
Time to retire your old waterproof and invest in a new one? This guide should help you navigate the plethora of waterproofs on the market
Designer Ronnie explains the benefits of regularly cleaning and reproofing your waterproof
Our step by step instructions for cleaning and reproofing your waterproof garment
Our waterproof jackets deal with water coming from the outside and the inside. Read this guide for tips on making the most of your waterproof's breathability.
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