What Does Waterproof Breathable Mean? 

"Waterproof Breathable"

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Is that Waterproof AND Breathable or is it Waterproof OR Breathable?

Gore-Tex, Neo Shell, eVent and other waterproof membranes are funny things. For many people it's the layer they reach for anytime the weather isn't perfect. The thing is that those waterproof breathable membranes just don't seem to breathe very well when it's wet out and as far as I can tell, nothing does. The problem is physics.

Okay, so I talked about membranes, what are those? There's two classes of waterproof jacket out there - membranes and coatings. Membranes work by bonding a membrane to an outer material (and often another layer or two) while coatings are just that - something basically slathered onto the outer material with maybe a protective layer or raised profile on the inside. Membranes - like Gore-Tex and eVent tend to breathe better, but the jackets also tend to be heavier, less packable and more expensive. Coatings - like Marmot's NanoPro or Pertex Shield+ are lighter, less expensive, but less breathable and often less durable that their membrane counterparts.

The Waterproof Breathable Problem

Waterproof breathable membranes and coatings work on the principle of diffusion. Diffusion needs a difference in humidity on each side of the membrane in order for your jacket to accomplish anything. The bigger the difference, the higher the rate of diffusion. When you are working hard, it's wet inside your jacket, so it's best at moving that sweat to outside your jacket when it's dry out. 

Pissing rain means it's pretty damn humid out - which means the driving pressure for diffusion is low or straight up zero which means maybe your jacket is waterproof, but it just isn't very breathable. If you are sweating while it's pouring raining, you're getting wet. If the humidity outside your jacket is the same as the humidity inside your jacket - then there's just nowhere for your sweat to go, so unless there's some crazy voodoo going on that I don't know about, I don't know how a breathable jacket could keep you dry while you are working hard in a humid environment. It's certainly what I've experienced during my time in the super wet coast mountains of BC. 

If you want more info on how waterproof breathable membranes and coatings work, REI has a really good article on it.

What it really comes down to, is if it's raining out, you have three realistic options: 

1. Say screw it to a shell, get wet from rain. Works when it's warm.
2. Wear a waterproof shell, work hard and get wet from sweat which is generally warmer than getting wet from the rain, but you freeze when you stop.
3. Wear a waterproof shell , realize that it's going to breathe like shit, even if you have the fanciest thing out there because the humidity inside and outside the jacket are so similar and restrict yourself to only going as fast as you can go without seriously sweating. If you start getting wet, slow down. 

Notice that there's no solution for 'stay dry while working hard in the rain'. There just isn't anything out there that can do that at this point.

The real reason to carry that waterproof-breathable jacket on a ski tour is for the way down - protection from snow while you're skiing - but do you really need to pay for the most breathable possible jacket to get that done?

The Alternative Solutions

I have a different way of doing things. In fact, I have two. The first is 'the two jacket system' and the second I call 'the honest compromise'.

I'm going to reference gear that's currently in the review-cue since I've got it lying around and have used it recently, but there's lots of options to everything.

The Two Jacket System

The two jacket system basically breaks the goal of your shells down into component parts - instead of using a jacket that is decent (at best) at everything, let's use one jacket that's super breathable and one that's waterproof.

This is the system I use in the summer for climbing, scrambling and general mountain fun.

The Breathable Jacket

There are some amazing wind shells out there. These things shrug off wind and even light rain thanks to DWR coatings. I've used the Patagonia Houdini and the Arcteryx Incendo recently and they're both featherweights that disappear into your pack and breath miles better than any waterproof breathable jacket out there that I've tried. They even handle short bouts of light rain without too much complaint. 

I'm currently reviewing the Outdoor Research Helium II. While breathable, it's not as breathable as a membrane jacket, but it IS just as waterproof. If it's currently raining, then how breathable something is really doesn't matter that much because nothing is getting past the simple fact that the humidity inside and outside my jacket is the same damn thing so just as much moisture is diffusing IN to my jacket as OUT.

Now, nothing says you can't bring a membrane jacket and if the humidity isn't 100% and it's only a light drizzle,  then yea, the membrane jacket is going to be more breathable, but the difference just isn't that big and some of the coating jackets are way lighter and pack way smaller. The extra size and weight for a membrane jacket may not be worth it.

The Two Jacket Bottom Line

By giving up on the idea of one jacket doing everything and going with two jackets - I have a breathable jacket when I need a breathable jacket and I have a waterproof jacket when I need a waterproof jacket. The real kicker is that the two jackets combined can be lighter and cheaper than a single membrane based waterproof breathable jacket.

The Arc'teryx Beta AR jacket is basically the standard against which all other waterproof breathable jackets are measured. It's light at 460g advertised weight and uses the latest Gore-Tex Pro membrane, but it's also expensive at an eye-watering $700CAD. You can save some money by going with the MEC Synergy jacket at 438g and $425CAD.

My current Two Jacket system uses the Patagonia Houdini as a wind layer that clocks in at a measly 102g advertised weight and despite being made by 'Pata-gucci' only costs $119CAD. For a waterproof layer, I'm currently trying the Outdoor Research Helium 2. As you'll see in the upcoming review, it happily keeps me dry, it's breathable enough that I don't need to immediately switch layers when the rain stops, comes in at a super light 180g advertised weight and only costs $220CAD.

The traditional waterproof breathable system clocks in at 460g and $700CAD on the high end and 438g and $425CAD on the low end. In comparison, the two jacket system is going to cost you in the neighbourhood of $340CAD and weighs 282g.

It's counter intuitive, but by going with two jackets, you ca save money, you can save weight and you can save space in your pack.

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Even if you just can't wrap your head around the idea of leaving your trusty Gore-Tex jacket at home, being willing to leave it in your pack until it's genuinely raining and using a lightweight wind shell when it isn't is going to make you more comfortable for any reasonably high output activity.

The Honest Compromise System

The Honest Compromise System is designed for the needs of winter mountaineers. It's a system that I've wanted to see for ages and thanks to the dead bird people, it's starting to be a real thing.

A caveat: this system really only works in the winter. Once you're dealing with actual rain, it's time for the two jacket system.

When you're ski touring, you need something that's breathable on the way up and waterproof. The thing is, your shell doesn't need to be waterproof everywhere. Snow doesn't settle on vertical surfaces the way rain does - so what you really want is a jacket that has waterproof shoulders and arms, but is super breathable elsewhere. Likewise for pants, a waterproof butt and lower legs is really nice, but most other places, breathable is what you really need.

This brings us to the honest compromise. I spent this ski season rocking the Arc'teryx Procline Comp jacket and I used the Lythic Comp pants for a couple of seasons. It strategically balances waterproof panels of Gore-Tex Pro where you need waterproof and a super breathable, and stretchy softshell where you don't.

The result is pretty awesome and I really like this as a solution for higher output winter activities. 

The Honest Compromise Bottom Line

With the honest compromise jackets you have a shell that breathes enough that in cooler weather at least, you don't need to strip off your shell on the way up and is waterproof where you need protection from snow. It's not suitable for rain, because that'll soak through the softshell panels, but in the winter it's pretty ideal. I've also used these compromise shells for ice climbing and they're pretty solid there too.

The rub, is that the jacket still isn't breathable enough for spring touring, you still need to use a wind layer if it isn't cold enough to keep your sweating at least a little bit in check. If it's a nice spring day with blazing sun and my main concern is wind, I'm still going with a wind shell, but for those mid-season days when it's puking snow and pretty crisp out, these are the one jacket solution.

They are an honest compromise - they trade 'waterproof' for breathable because you just don't need 100% waterproof most of the time in the winter and the result is better because of that honesty. I really hope other brands jump on this trend.

The Waterproof Breathable Reality

I worked in retail for years and in that time I could not count the number of people who brought in a brand new Gore-Tex jacket and told me it was defective because they got wet while wearing it in the rain. The jacket was waterproof - but because there wasn't enough of a difference in moisture on each side of the membrane, the diffusion required to keep that person dry from sweat just wasn't there. 

For low energy output activities like light hiking - you can get away with a single waterproof breathable jacket. For high energy output activities like ski touring, a waterproof breathable jacket just isn't going to breathe well enough for most people. If rain isn't actually a worry, then be honest about that and ditch the waterproof and go with breathable with strategic regions of waterproof. If rain IS a worry, then either go slow, or get wet.

Breather membranes (also known as breathable membranes) reduce the chance of damp and mould forming in a building. They are installed in external walls and roof structures to prevent water ingress, but their vapour-permeable quality allows moisture to escape. A breathable membrane helps with ventilation and effectively allows a building to breathe.

Table of contents:

• What is a breather membrane and why are they needed?
• What is the difference between a breather membrane and a vapour control layer?
• Do I need a breathable or non-breathable membrane?
  • Breathable membrane
  • Non-breathable membrane 
• How to choose the right breathable membrane
• How to install a breathable membrane 

What is a breather membrane and why are they needed?

Breather membranes help to insulate your property, while protecting it from an array of external issues, including insects, dirt and weather penetration. With the demand for high thermal efficiency gaining traction, modern homes must be airtight and have a well thought out ventilation plan to ensure moisture levels are managed correctly. Condensation is a particular concern, and installing a breather membrane will help the building to breathe and allow moisture to escape.

The membrane itself needs to be fitted to the outer side of the insulation. Typically, they’re fairly easy to install and detailed installation instructions are usually found on each roll.

What is the difference between a breather membrane and a vapour control layer?

Breather membranes and vapour control layers (VCL) help to minimise condensation issues in your home. The terms are often interchanged with each other but actually perform two separate functions in a property. While the tasks they perform are similar, it’s important to note the different behaviours of each material:

• A breather membrane has a dual purpose; it allows vapour to escape from inside while preventing water ingress from outside.
• A vapour control layer minimises the amount of warm, moist air entering a property.

There’s a slight difference in where they’re placed within a construction too. A breather membrane is positioned on the outer side of the insulation, while a VCL sits on the inner side of the insulation.

Do I need a breathable or non-breathable membrane?

Breathable and non-breathable membranes share the same primary functions. They both prevent water ingress, reduce the chance of damp and mould problems, and are also resistant to cold winter weather. So, why do you need to choose between the two?

Breathable membrane

Breathable membranes allow a property to breathe by letting moisture escape through it and out of the building. It has a low resistance and is newer than its non-breathable counterpart, leading to a surge of interest in recent years. A breather membrane works well when positioned below slate or tiles, as it allows a good amount of moisture transfer, but it’s important to have adequate air movement above.

Non-breathable membrane

Non-breathable membranes are not air-permeable. However, they’re still widely used and are well suited to roofs which have existing ventilation installed. A non-breathable membrane offers high resistance and therefore only really suitable for installation in cold, ventilated pitched roofs. It’s important not to mix this type of membrane up with a VCL, which is positioned on the warm side of the insulation to prevent large amounts of moist air from entering the property.

How to choose the right breathable membrane

When it comes to choosing the right breathable membrane for your property it’s important to familiarise yourself with the British Standard for Slating and Tiling BS . This code of practice covers new-build pitched roofs and vertical cladding. It was updated in to recognise the way breather membranes are selected depending on their positioning and the type of building they’re being installed in. This largely relates to air pressure within the membrane that can ‘balloon’ causing pressure on the underside of the roof covering, which could dislodge slates and tiles.

The amendment to BS provides guidance on installing breathable membranes in particular geographical locations, due to the wind pressure in different zones across the UK. Consequently, manufacturers must state which zones their product is suitable for.

A further key consideration is the type of building you’re installing the breathable membrane in. It’s likely the membrane will receive added pressure if it’s installed in an outbuilding such as a garage or carport, or if the site is by the coast or in excess of 100m above sea level.

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How to install a breathable membrane