How do waterproof fabrics work?

Finding a fabric that blocks rain is easy. Even normal plastic bags and ponchos can block the rain. But your rain gear’s fabric must block rain while allowing your sweat to escape. As you will be using your waterproof jacket while hiking, trekking, running, etc, the fabric needs to block water and wind and must provide some level of breathability.

In conclusion, the waterproof fabric of a jacket is made in such a way that large molecules like water can’t get in but smaller vapor molecules, from your sweat, can get out. 

Outer Layer: Most waterproof fabrics are composed of face fabric (outer layer) that is the exterior part of the fabric. It is what you see when you put on the jacket. The face fabric is treated with DWR (Durability Water Repellency) coating. This is the first line of defense from rain as it makes water bead up and run off the jacket. This DWR won’t let water penetrate through the face fabric of your jacket. 

Inner Layer: The layer below the face fabric is the waterproof membrane. This waterproof membrane is not visible to us because it is sandwiched between the face fabric and an inner layer or ‘scrim’. This inner layer or scrim is closer to your skin. 

The purpose of the scrim is to absorb your sweat and moisture outwards and protect the waterproof membrane from contaminants such as sweat, body oil, lotions, etc. 

The construction and nature of this inner layer determine whether a fabric is 2, 2.5, or 3-layer.

Understanding the Fabric Tech: 2 Layer vs 3 Layer

You may have heard shop keepers and brands talking about 2 layers, 3 layers while explaining their jacket features. It’s also written and called 2 L, 3 L or 2 ply, or 3 ply.

Layer in a waterproof jacket/trouser refers to the number of bonded layers within the outer shell fabric of the jacket. It is the construction of the waterproof fabric. 

There’s a misconception among buyers and sellers in Nepal that the layer refers to the inner lining or filling of the jacket. 

If a jacket is filled with down or synthetic & polyester insulation for warmth then it has a filling. 

A jacket has a lining when a layer of material is added for durability, breathability, or to cover the filling or inner layer of the fabric. The materials could be silk, taffeta nylon, mesh (net), etc.

 2 Layer

If a jacket is 2-Layer then it means that a protective inner coating is bonded to a face fabric like nylon or polyester. The second layer is generally made up of polyurethane (PU) or expanded polytetrafluoroethylene (ePTFE) and its purpose is to wick sweat away from the wearer’s skin or inner clothes and also to prevent water from seeping in. 

The first layer i.e. face fabric makes water bead up and run off the jacket due to DWR whereas, the second layer provides breathability.

Oftentimes, you will hear about the 2.5 Layer. In this, a printed or sprayed-on partially protective layer is applied over the 2 layers.  This 2.5 layer protects the waterproof membrane as body oils, sweat, sunscreen, lotion, etc, can contaminate it and degrade performance.

Pros:

A jacket with a 2 or 2.5 layer is lightweight, is packable and you will feel comfortable in it as it is made from a flexible material. It doesn’t make the wearer feel bulky and doesn’t restrict the freedom of movement. Example: Aroan’s ‘Monsoon-Summer Anorak’ and ‘Royal Blue Monsoon Cyclone Parka’

Cons:

2 Layer fabric isn’t as breathable as 3 Layer. And it’s not as durable as it lags scrim or tricot fabric bonded to the waterproof membrane. 

3 Layer

Outer face fabric, waterproof membrane & inner are bonded together into one flexible material and it looks, feels, and works like one layer. As the name suggests, these waterproof fabrics are made from 3 layers that are laminated together. 

The waterproof-breathable membrane is sandwiched between an outer face fabric and an inner layer, most commonly a lightweight tricot fabric or a scrim (gridded polyester). This scrim or inner layer protects the waterproof membrane as it adds some texture and durability. 

Pros: 

Waterproof jackets made from 3 layer usually offers superior protection from the elements (wind, rain, snow) and they have a longer life because of the presence of the scrim/tricot fabric protecting the waterproof membrane. It also offers the highest level of breathability as moisture/sweat is transferred from the skin outwards most effectively.

Cons:
Because of the addition of a 3rd layer, 3 Layer waterproof jackets tend to feel heavier and bulkier. It is less flexible than a 2 Layer waterproof jacket is usually stiffer and crispier.

The importance of DWR coating

DWR is a durable water repellent coating used on waterproof fabrics. When water hits the surface of a new waterproof jacket or raincoat, this DWR coating makes water bead up, and runoff.

Waterproof fabric with a smooth and shiny surface has an excellent DWR finish, whereas waterproof fabric with a cotton finish on the face fabric has a decent DWR.

With time and because of poor maintenance, DWR coatings become less effective due to the accumulation of dirt, dust, sunscreen, sweat, and smoke from the campfire. 

You can know the DWR coating on your waterproof jacket or your raincoat has become less effective if water soaks into the face fabric instead of just beading up and rolling off. 

Once the DWR finish wears off, water is absorbed into the fabric, which creates the ‘wet out’ effect. This is the time when you need to revive your rain gear’s DWR.

Seam Sealing

Using a waterproof fabric, a waterproof jacket can be made however it isn’t completely waterproof unless the seams have been sealed. Without the seam sealing/taping, water will quickly enter inside the jacket through the holes created by needle stitching. 

You can check whether your waterproof jacket has sealed seams or not by looking inside the jacket. If you see strips of tape covering the seams, then the jacket has sealed seams. In case, there’s a cloth lining inside or a filling that blocks the visibility of the seams then you can touch and move your fingers on the outer seam area. If you feel that the seam area is stiffer then you can be certain that your waterproof jacket’s seams are taped/sealed. 

Ventilation

As the seam taping won’t let rain enter through the jacket nor let excess heat and moisture (sweat) escape, ventilation is needed somewhere in the jacket. Monsoon Cyclone Parka has under-arm ventilation near the back to ensure breathability. 

Water-Proof Zippers

A waterproof jacket with a normal front zipper won’t be enough if you walk into a rainstorm. Water will get through your jacket from this zipper and reaches your inner garment and skin and soaks you. 

While buying a waterproof jacket, it’s best to look for the ones with Waterproof zippers. Waterproof zippers have rubber or PVC coating covers on the front of the zip that covers and hides the coils (teeth) of the zipper. When this zipper is closed it makes the jacket completely waterproof and windproof.

Some Technical Terms

Gore-tex 

Most big brands such as Arc’teryx, Patagonia, and The North, Mammut often use Gore-tex in their products. Robert Gore invented a waterproof/windproof breathable fabric membrane in 1969 by yanking a material called PTFE, the polymer stretched by 1,000% to create a microporous structure. This fabric and technology were later named Gore-tex. 

GORE-TEX® membrane has up to nine billion pores per square inch. These pores are 20,000 times smaller than a water droplet but still 700 times larger than a water molecule. This structure and fabric tech allows sweat and water vapor to escape through the fabric while keeping out rain and snow. 

Shell: 

Shell is the outer layer of a garment. Much like with an egg, the ‘shell’ is the tough exterior that keeps the elements away from you.

Hardshell:

Stiffer outermost layer made from waterproof fabric that is durable and can withstand heavy rainfall, snow, and wind. 

Softshell:

Softer fabric such as polyester and nylon. Provides more breathability and flexibility but won’t provide protection against the rain and wind like a hardshell jacket. Great to be worn on a dry day for high-intensity activities.