Waterproof ratings and breathability explained
Waterproof and breathable fabrics will keep you dry and comfortable, so what does waterproofing actually mean? And what are all those numbers?
Here’s everything you need to know about waterproofing and breathability.
SO WHAT DO THESE NUMBERS ACTUALLY MEAN?
These numbers indicate how waterproof a fabric is, measured in millimetres. Using the first rating, 5,000mm, as an example, if you were to put a square tube with inner dimensions of 1” x 1” over the fabric, you could fill it with water to a height of 5,000 mm before water would begin to leak through the fabric. So, the higher the number, the more waterproof the fabric.
You’ll often see another number alongside these, expressed in grams. This number is how breathable the fabric, found by testing how many grams of water vapour can pass through a square meter (m2) of the fabric from the inside to the outside in a 24-hour period. In the case of a 5,000g fabric, this would be 5,000 grams. The larger the number, the more breathable the fabric.
CAN OUTWEAR BE FULLY WATERPROOF?
Although fabrics can be fully waterproof, such as rubber and wax, outwear for active sports will usually be varying degrees of water resistant, as with enough water, wear, and pressure, it will eventually leak.
It’s important active outerwear retains an element of breathability otherwise you’ll keep the water out but soon be wet from your own perspiration. As a result, most outwear balances protection with breathability.
If you ride only occasionally, using lifts and pistes, rarely or never hiking or climbing then breathability doesn’t need to factor quite as highly in your decision. You probably won’t work up enough of a sweat to justify the higher price point. However, if you’re a more serious backcountry rider this rating will become more important.
HOW DOES IT WORK?
Waterproof and breathable fabrics have an outer layer, known as ‘face fabric’ made from nylon or polyester and a laminated coating. This layer is designed to look stylish and offer protection in the form of a treated solution called DWR (durable water repellent) so it doesn’t soak up water.
Instead, the waterproofing is left the next layer, the membrane, which is made of tiny holes too small to let water in, but large enough to allow water vapour to escape. Contamination with oil, sweat, and other chemicals causes the membranes to lose their ability to keep out water, the membrane is protected by an ultra-thin layer of Polyurethane (GORE-TEX® membranes have a bi-component laminate structure) or other oleophobic (oil-heating) treatment (eVent™ does this at the microscopic level with individual PTFE fibres).
A fine scrim or mesh is then bonded to the inner surface for comfort in 3 layer fabrics. 2 layer fabrics receive a separate fabric liner, while 2.5 layer fabrics use an abbreviated pattern screened on the inner surface to save weight.
Modern waterproof breathable fabrics have come a long way since the original GORE-TEX®; now, most are extremely waterproof at any price point, but huge gains in breathability in the past few years have redefined the market in high exertion outerwear.
Sitting alongside their waterproof and breathability ratings, these fabrics are also typically classed in layers; either 2 layer, 2.5 layer, or 3 layer, often abbreviated to L.
This is the most commonly used construction for waterproof outerwear. Typically this construction will use the same fabrics and membranes as 3 layer but without a bonded layer on the inside, instead using a mesh or loose fabric lining.
Although 2 layer fabrics can offer the same waterproofing rating as a 3 layer, they’re often bulkier and heavier with the looser layer inside. One of the benefits however is their cheaper price point.
2.5 layer fabrics don’t have a bonded mesh lining or a separate sewn-in lining, but include a very fine raised pattern screened onto the membrane to keep it off your skin. The raised pattern helps to protect the laminate from your body oils, sunscreen, bug spray, and anything else that can break down the material over time.
Most commonly found in rain shells, this fabric can also be used for winter sports too. Like 3 layer fabrics these can be lightweight and easily packable.
3 layer fabrics are constructed with an outer layer, or ‘face fabric’, usually made of nylon or polyester and a ‘membrane’ that’s bonded to it; membranes are the waterproof layer. Then, a very lightweight backing fabric is attached to the interior. It’s not loose hanging like a 2 layer, and helps to improve comfort by absorbing moisture and helping transport it through the membrane and to the surface of the face fabric. The interior lining also helps protect the waterproof laminate from being dissolved by skin-borne substances.
This is the most advanced construction offering a protective, lightweight, durable, and most importantly breathable fabric, but it comes at a price.
SO HOW WATERPROOF DOES YOUR OUTWEAR NEED TO BE?
A minimum of 5,000mm is good for both skiing and snowboarding in cold but clear conditions, especially if you enjoy taking regular breaks. 5-10,000mm is ideal for those who spend long days out on the mountain, in all weather conditions; while 10-20,000mm is best for those in wetter climates, or skiers and snowboarders you prefer backcountry.
WHAT IS SEAM SEALING?
Seam sealing, or seam taping, covers the tiny holes made by sewing such as around zips and pockets, so they don’t leak. This process is usually done using a heat application of thin, waterproof tape.
The alternative to sewing is welding or bonding, which attaches the pieces of fabric together using heat-activated film. Bonding can be lighter and less bulky but can become costly.
Sewn seams tend to be a little stronger so often brands will use both methods when producing their garments; sewn seams around stress-bearing areas such as arms and legs and bonded for pockets and zippers.
Outerwear often comes in different levels of taping from ‘fully taped’ to ‘critically taped’. On fully taped garments every seam has been made waterproof whereas critically taped garments usually only have ‘high exposure’ areas taped such as the neck, shoulders, and chest.
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