Your expensive jacket can be one or the other, but not both at the same time
Waterproof fabrics have seen plenty of development in recent decades, but are their capabilities being overplayed?
Almost every brand promises their waterproof jackets can lock out water on rainy days yet still allow sweat to ‘breathe’ through, to prevent you getting soaked from the inside.
Is this possible, though?
And if your current waterproof jacket isn’t all it’s cracked up to be, is there anything you can do to stay dry and comfortable when cycling in wet weather?
To answer these questions, we spoke to three experts on waterproof fabrics; Charles Ross, lecturer and specialist in performance sportswear design at the Royal College of Arts, Thomas Plummer, head of apparel at Madison, and Tim Wilson, managing director of Storm Care.
How modern waterproof fabrics were invented
Before we get to why common waterproof fabrics may not work exactly as advertised, let’s take a look at how modern breathable waterproof materials were invented and how they function.
In 1958, Bob Gore (of Gore-Tex fame) created expanded polytetrafluoroethylene (ePTFE).
Gore’s father, Bill Gore, had worked at DuPont, the American chemical company, where standard PTFE – or Teflon as it was later branded – had been invented 20 years earlier.
Working with his father, Bob discovered that if you vigorously stretch PTFE it expands rapidly and forms a microporous structure.
According to Charlie Ross, a typical ePFTE membrane contains around “a million holes per square inch”.
The tiny size of these holes means ePTFE is permeable to microscopic particles of water vapour, but impermeable to larger water droplets – hence the claim it’s ‘breathable’ and waterproof.
To create a fabric from which garments can be constructed, an ePTFE membrane is sandwiched between two layers of nylon or polyester fabric, to help protect the membrane from abrasion and dirt.
This forms what’s commonly referred to as a ‘triple-layer’ (sometimes called a ‘3L’) waterproof fabric.
On these fabrics, the outermost layer is typically coated with a Durable Water Repellent (DWR) coating, designed to prevent the fabric saturating with water – or ‘wetting out’ as it’s commonly called.
A fabric ‘wetting out’ is a problem because having a layer of water on the outside of the fabric blocks the transfer of water vapour from the interior of a garment to the exterior, as the humidity on the outside of the fabric effectively becomes 100 per cent.
So far, so good, then, but this belt-and-braces approach isn’t without its drawbacks.
Primarily, DWR coatings wear out and need to be refreshed over time – and, if neglected, waterproof fabrics tend to ‘wet out’ much quicker. This is why specialist detergents and cleaners from brands such as Storm Care and Nikwax exist.
In late 2015, though, Gore unveiled Shakedry, a two-layer fabric with the ePTFE membrane on the outside.
Eschewing the outermost layer made for a lighter fabric, but it also negated the need for a DWR coating – because the hydrophobic nature of the ePTFE membrane didn’t require one – solving the issue of such coatings degrading over time.
Why Gore-Tex isn’t magic
According to the brand and many testers (including here at BikeRadar), Shakedry set new standards for breathable waterproof materials.
However, it’s vital to appreciate how such materials ‘breathe’ in order to understand how they work, and, perhaps more importantly, how they don’t.
It is true that an ePFTE membrane can simultaneously be impermeable to water and permeable to water vapour. However, the conditions under which water vapour will diffuse from one side to the other are specific and, typically, don’t occur when you need them most.
As with any gaseous diffusion, waterproof membranes rely on a partial pressure gradient to transfer water vapour from one side of the fabric to the other.
For your sweat to ‘breathe’ through the fabric of a waterproof jacket, for example, the air outside the fabric must be less humid (meaning it has a lower concentration of water vapour) than on the inside.
When it’s raining, though, Ross says “the outside humidity can be 85-90 per cent”, meaning the air is almost completely saturated with water vapour.
As a result, there isn’t a partial pressure gradient between the inside and outside of the fabric, and water vapour can’t ‘breathe’ out from within until the humidity inside builds to the point that one is created (by which point you will, by definition, be very sweaty).
In reality, then, ‘breathable waterproof’ fabrics are both ‘breathable’ and ‘waterproof’, but not at the same time.
They can ‘breathe’ when it’s dry and keep water out when it’s wet – but if you’re working hard enough to induce sweating when it’s humid outside, you’ll still get wet on the inside, no matter how expensive your waterproof jacket is.
Even on dry days, though – when ePFTE membranes breathe best – Ross says you’ll likely be better off with a windproof jacket than a waterproof one.
This is because windproof jackets are typically made solely from woven fabrics (with correspondingly larger holes between the fibres) and don’t feature a waterproof membrane.
How incoming PFC bans will affect waterproof clothing
Making matters more complicated, both the European Union and United States have recently placed restrictions on the manufacturing and use of perfluorinated compounds (PFCs) – the stuff that PTFE, ePTFE and DWR coatings are also typically made from.
These chemicals (often referred to as ‘forever chemicals’ because they don’t degrade in the natural environment) can be highly toxic under certain circumstances, with links to cancer and a range of other ailments.
As a result, most manufacturers of waterproof garments are phasing out the use of PFCs where possible.
Gore, for example, says it “has set the goal of eliminating PFCs of Environmental Concern from the life cycle of its consumer fabrics products”.
According to Gore, “PFCs of Environmental Concern” are “highly fluorinated, small enough to be bioavailable, and persistent.” It says this definition was agreed in accordance with Greenpeace.
Notably, Gore doesn’t include its ePTFE membranes in this category, though. It argues ePTFE is chemically inert and therefore isn’t toxic (something Ross echoes). Given this, it will continue to produce its traditional ePTFE membranes for use in waterproof gear.
Many influential brands are moving towards PFC-free solutions as they seek to produce more environmentally friendly products.
With that in mind, Gore developed a three-layer waterproof fabric with a ‘PFC-free’ expanded polyethylene (ePE) membrane and a PFC-free DWR treatment in 2021, which is used by brands such as Adidas and Patagonia.
Pertex’s Shield waterproof fabric, meanwhile, is made with an expanded polyurethane (ePU) membrane. This fabric is used by brands such as Albion and Altura.
According to Pertex, the breathability of its ePU membrane “is dynamic” and “rises as the output of the user increases” (as long as the outside air is dry enough to allow water vapour to diffuse from inside to outside of the jacket, we presume).
Wilson says that, initially at least, riders are likely to see a reduction in performance from such ‘PFC-free’ garments compared to existing ones, particularly with regards to how long the factory-applied DWR treatment will last.
As a result, owners of such gear should expect to maintain or rejuvenate the DWR treatment on a PFC-free jacket more frequently (check out our guide to reproofing your waterproof cycling gear if you need a refresher on this).
He also says PFC-free waterproof fabrics could be less durable and resistant to contaminants such as dirt and oil.
This in particular, Plummer says, is a cause for concern because riders may feel the need to replace their gear more often if it wears out or simply looks tattier more quickly – something that wouldn’t be good for the environment either.
However, he also says performance of PFC-free waterproof fabrics should improve over time, as brands develop new technologies and products.
What does this all mean for cyclists?
While we’ve come a long way from traditional waterproof fabrics that offered no breathability whatsoever, there’s no escaping physics.
A waterproof fabric will keep water out when it’s raining, but, if you can, it’s probably best to avoid getting too sweaty when cycling in wet weather.
That may mean opening up zips or vents while climbing, for example, to increase ventilation and dump heat when you don’t need it.
Jackets with mechanical ventilation, such as mesh panels or zippered vents, can also help improve ventilation.
For riding in changeable conditions, or if you know you won’t be able to avoid working hard on a ride, though, it’s also worth considering whether a traditional hardshell waterproof jacket is the best option.
In these scenarios, a softshell jacket or jersey with a water-repellent fabric may be a better option for keeping you warm and comfortable.
Castelli’s latest Gabba R jersey, for example, features a hydrostatic head rating of “over 5,000mm” – that’s more than the 1,000mm rating required by the International Standards Organisation (ISO) for a ‘waterproof’ fabric, but it's far less than a typical triple-layer waterproof fabric.
The top-rated entry (Endura’s Pro SL Shell Jacket II) in our guide to the best waterproof jackets, for example, has a waterproof rating of 20,000mm – four times that of the Gabba R.
The upshot, though, is that the Gabba R’s fabric is claimed to be far more breathable (as well as more aerodynamic, thanks to its stretchier fit).
In our experience, unless it’s absolutely pouring, these kinds of garments can keep you ‘dry enough’ yet don’t lead to you overheating or getting wet from sweat on the inside.
It’s no surprise, therefore, that many professional riders often reach for garments in this vein for racing in tough conditions.
Likewise, if you already have an expensive waterproof jacket made with PFCs, then fear not – like the Teflon in a non-stick pan, these are still considered safe to use under normal circumstances.
While it may have been made using some nasty chemicals, the best thing all of us can do to protect the environment is to look after and keep using the kit we already have.
After all, if you discard a PFC jacket in favour of a new ‘eco-friendly’, PFC-free one, that old jacket doesn’t just magically disappear – the ‘forever chemicals’ it's partly made from will still exist somewhere.
If you don’t have a waterproof jacket and want or need to buy one, then you might also consider shopping second-hand. Often, a wash with re-waterproofing solution and a quick spin in a tumble drier can breathe new life into old waterproof fabrics.