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The GO Outdoors Guide to Waterproofing and DWR

Simply put, waterproofing is a garment’s ability to resist water and moisture. 

Tested in lab conditions to keep out a certain amount of water, waterproofing has set standards by which it can be meaured. 

 All garments sold in the UK are sold in waterproofing levels known as PSI, or Pounds Per Square Inch, or measured in a Hydrostatic Head (see below).

 

Measuring Levels Of Waterproof by Testing

The Water Column Test /Hydrostatic Head Test

This is a test in which a tube of water 1" in diameter is filled with water.
The fabric is held taut underneath this (sealed) column of water. 
This is then tested over 24 hours to see how many millimeters of water the fabric can withstand before leaking. 
When the fabric begins to seep water, the mm is noted as a score, and this is known as the ‘hydrostatic head’ which literally means:

Hydro –Water
Static – Not moving
Head – Height

PSI (Pounds per Square Inch)

The PSI relates to the amount of water pressure that a garment can withstand both from the pressure within the garment (the wearer) and the external conditions (the weather). PSI can also be converted into mm of pressure for a simple reading. 

 To be 100% waterproof, the British Standard of 3 PSI has to be met, which can withstand 1500mm of pressure.
 However most garments typically exceed this level - and are often made at 40 PSI. 

Generally, the higher the PSI, the more effective the waterproofing will be. However the higher the PSI level and the more effective the waterproof is, the more expensive the garment will be.  

 

Creating A Waterproof By Using Fabrics

Although there is a huge range of waterproofs with different names, and different levels of performance, they fall essentially into two different types: 

 

Coated, Breathable Membranes - Fabrics Created with a PU Coating and a Membrane construction to Waterproof them.

  • These are manufactured by spreading a thin layer of resin directly onto the inside face of the fabric, also known as a hydrophilic coating. 
  • Fabrics are sprayed with a PU (Polyurethane) coating before being made into a jacket. 
  • The seams are then sealed to prevent moisture entering the garment in any way.
  • Hydrophilic coatings rely on the behavior of water molecules so heat generated by the body inside the garment drives body moisture down the polymer chains in the coating to the external face.
  • This is also known as moisture management. Most membranes rely on a pore based construction, so as well as being waterproof, they can also vent out hot air and sweat. 

Durable Water Repellency (DWR)-  A Waterproofing Treatment Sprayed Onto The Face Fabric

DWR is Durable Water Repellency, another way of coating the fabric after a laminate or membrane has been applied to form a protective wall from water droplets on the outer layer. 

A chemical treatment, DWR is not waterproof, but does reduce condensation forming, aiding breathability so less moisture reaches your skin. 

DWR needs to be reapplied, and can be retreated to improve it’s performance. Due to DWR being applied to the face of the fabric, it is easily affected by dirt and oils, which soon coat the DWR layer, hindering the performance.

 DWR can also be removed by regular cleaners, so DWR should always be treated with a specific product which can refresh it.

 

Examples Of Other Waterproof Treatments For Fabrics

As well as DWR, many companies have their own water repellent fabrics applied to the face of the garment such as:


Lowe-Alpine Triple Point

A multi-layer, lightweight coating, more suitable for general walking than more demanding outdoor sports. The outer face of the fabric has a standard DWR treatment applied to it to enhance performance. 

The process leads to very high performance in terms of breathability and durability. Durability, in particular, is enhanced by the residue of ceramic particles that remain in the fabric. Items made of Lowe Alpine Triple Point are incredibly tough and extremely hard-wearing.

 

Lowe-Alpine Triple Point Ceramic.

A multi-layer microporous coating, during the construction of which the coating is impregnated under high pressure with millions of ceramic particles, which has the effect of creating microscopic holes around each particle. A special near-permanent Dry Yarn technology treatment is then applied to the fabric’s outer face to improve performance.

 

Mountain Equipment Drilite

A fabric that exists in both coated and membrane form. In membrane form it is called DLE.

 

Examples Of Waterproof Membranes Within Fabrics

Breathable Membranes e.g GORE-TEX, e-Vent

Breathable membranes consist of an extremely thin film containing microscopic pores that are large enough for body moisture to pass through, but small enough to keep water droplets out. Most microporous membranes are laminated to a face fabric and are available in two- and three-layer versions. 

A plastic based PTFE (Polytetrafluoroethylene) layer is laminated to the outer fabric and then the garment is cut to shape. Seams are then sealed for complete protection. A membrane jacket will out-perform a coated waterproof by about 25-30% greater efficiency on moisture movement and control.

 

GORE-TEX

GORE-TEX is the most established brand of microporous membrane. It consists of a wafer-thin expanded PTFE - Poly-tetra-fluoro-ethylene (Teflon), in which each pore is 20,000 times smaller than a water droplet, yet some 700 times larger than a body moisture molecule. The fabric thus has excellent levels of waterproofing and breathability. It is laminated to either one or two surfaces, the different processes then being described as two- and three-ply.


 

Other Variants of GORE-TEX

GORE-Tex XCR, or Pro Shell  is GORE-Tex which offers supreme levels of abrasion resistance. Created with a three layer construction including a taffeta lining which helps coat and surround the inner membrane, GORE-TEX XCR/Proshell is designed to be lightweight as well as extremely hardworking, with more breathability than the traditional 2 layer Gore-tex style, but is often slightly more costly.


 Three-ply GORE-TEX is more durable as there is no friction on the actual membrane and it is completely protected.

 A two-ply GORE-TEX is more durable than a one layer creation, yet the fabric is more susceptible to abrasion on the inner surface than a three ply or XCR GORE layer.


 

Advanced Moisture Management - Paramo

This is a membrane where the outer layer sheds most of the water. When water penetrates the outer it comes into contact with the “pump liner” or drop liner, which forces any moisture back out of the jacket. The “pump liner” effectively dries faster than it can get wet as the waterproof element is within the lining. 

 Paramo works like the fur of an animal whereas conventional waterproofs work more like a sheet of plastic. There are three constituent components: two layers of fabric and a waterproofing agent. The fabric is impregnated with Nikwax TX Direct treatment that leaves a water-repellent finish on each individual fibre so that the outer layer, as well as being fully windproof, will deflect at least 90% of water that hits it. 

This unique system of water transfer control, insulation and waterproofing is derived from observations of how an animal’s fur works. The inner layer is a very short-haired fleece which is reversed, so that as water enters the fleece and moves down towards the base of the fibres, it comes under increasing pressure; eventually it cannot get any further and is pushed back up the fibres. 

In addition, the waterproofing treatment causes the garment to treat water directionally, so that any water that hits it is deflected. It also means that any moisture that is created on the inside will be drawn away.

 

Advantages of Paramo

Paramo is extremely breathable: no matter how hard the wearer works, or how much they sweat, body moisture will be moved away. Due to the way it functions, and the type of fabric used, fewer layers of clothing are required underneath. Paramo jackets do not appear to have a finite life: as long as they are periodically reproofed (about every 12 months) by washing with either TX Direct or Granger’s Extreme and then tumble-dried, they will keep on working. 

 For comparison, a Gore-Tex or other membrane jacket will have about an eight-year life and a coated jacket five or six years, before they are worn out. Punctures do not harm the material and rips can be easily repaired.

 

Disadvantages of Paramo:

The material is comparatively heavy. It is questionable whether it is sufficiently durable to be recommended for serious mountaineering use. It has no hydrostatic head. When it needs reproofing water can be pushed through the fabric, e.g. by the weight of a rucksack; however the water will disappear soon after the pressure is released.

 

Pile/Pertex

The outer shell of a waterproof garment can be made with Pertex, a close-weave synthetic fibre that is inherently windproof, and DWR-treated to improve water resistance. Any water that does get through will not make the wearer cold since it is warmed up upon meeting the body heat of the wearer within the fibres of the inner. The water transmission system is driven by the wearer’s body heat.

 

The advantages of Pile/Pertex:

It is extremely effective at keeping the wearer warm and dry, even after being put on when the wearer is wet. It can be worn on its own or over a simple base layer.

 

The disadvantages of Pile/Pertex:

The system only works effectively within a temperature range of +5ºC to –10ºC. If the wearer is immobile for a prolonged period, and the garment is wet, it will draw away body heat in order to dry itself.

 

e-Vent:

e-Vent fabrics use a membrane composed from pore based technology as seen with GORE-TEX. 

However e-Vent differs in that it does not use a PU layer. This is designed to speed up the process of evaporation, by removing the need for a two step transfer process. For this reason, e-Vent is highly breathable as well as waterproof.

 

Reproofing Waterproofs to Enhance Performance

Washing and reproofing your waterproof items will improve their performance and longevity. This should be the use of gentle cleaners so that the weatherproofed coatings are not stripped off (with DWR) and so pores stay unclogged (as with membranes such as GORE-Tex and e-Vent).

You should retreat your waterproof garments every 4-6 months, depending on usage. Washing and applying heat (either via a tumble dryer or iron) revitalises the water repellency of the treatment. 

Waterproof garments can be treated with a wash-in product in the washing machine, or a spray-on solution. Sprays are best suited for coatings, whereas wash-in treatments work best with membranes. 

Cleaning agents need to be non-detergent based, in order not to affect the waterproof coating on the fabric.

 

Nikwax Tech Wash

It is a non-detergent soap that will clean the fabric without affecting the coating it has on it.

 

Nikwax TX-Direct Wash-In

TX 10 is a wax-like elastomer suspended in water.

 

Granger’s Extreme Wash-In

It contains a flouro-chemical and is water-based. It’s recommended by GORE-TEX products. The garment is washed and then treated with the products in the washing machine. 

The treatment is fixed and activated by heat so the garment is finished by either tumble-drying or ironing on a low setting.

 

Waterproofing By Design - Typical Features

Clothing

  • Adjustable cuffs are common on jackets and waterproof clothing as they close off the sleeves, one of the main access points for water to enter. Full storm flap protection on all openings.
  • Sealed seams- These indicate that the closures of the garment are fully stitched to prevent water leakage
  • High cut collars 
  • Inward facing zips 
  • Water resistant and reinforced shoulders and elbows
  • Snow skirts (optional). 
  • Cinch-in waists and hem drawcords, cuffs and collar that can be adjusted. 

Footwear

Moisture wicking liners are included in most shoes such as running shoes as well as walking boots, and membrane technology is typically used, such as e-Vent or GORE-Tex. 

As well as being fast cooling, these membranes offer absolute waterproof protection. Synthetic uppers are used to protect the whole foot from moisture.

 

Tents

  • As well as being able to withstand the pressure of rain, any waterproofing item needs to be sealed to prevent rain and moisture entering. The majority of tents are made from polyester, and the vast majority rely on a PU (polyurethane) coating to make them waterproof. 
  • These coatings come in different strengths, measured in Hydrostatic Head (hh). 
  • The higher the hydrostatic head the more waterproof the material and the longer the waterproof coating will last. 
  • For a tent to be classed as waterproof it must have a HH of at least 1500. 
  • Flysheets can go up to and beyond 5000hh, while ground sheets can be even higher.

 DWR - Durable Water Repellent


DWR is a water repellent coating added at the manufacturing stage to a product. Usually DWR is used not only used to help repel water, but to increase breathability.

Typically a DWR treatemnt is used in conjunction with a weatherproof membrane (such as GORE-Tex or e-Vent) in order to achieve high levels of breathability and weatherproofing.

DWR is a factory applied coating, but it is expected with any DWR treatment that over time you will need to re-proof it. Often, the breakdown of the DWR treatment, cuased by oil build up and general wear causes a waterproofed item to begin to leak, even if it's made from a high qulaity membrane such as GORE-Tex. 


DWR is made using fluorpolymers in most cases, and these coated to the face fabric. They work in a way that is similar to Teflon in a non stick pan, allowing moisture to bead off. 

A garment made with a coating of DWR is usually cheaper than a pore based weatherproof membrane, and offers a good level of protection on slimmer items (e.g. packable jackets) which is why many choose it. 

 Ideally you should look at DWR treatments as a way to improve or enhance existing water resistance. 

This guide explains how and when to apply DWR treatments to get the maximum benefits from your weatherproofed items. 

 

DWR Application

DWR is applied at the manufacturing stage, laying directly onto the individual fibres of a thread, which is crucial in helping the garment to allow water to bead off, without hidering breathability. The factory applications are more thorough than a home coating, and seams are typically sealed as well to allow 100% waterproofing. 

Sealed seams are a method of coating the seams of a garment to cover the microscopic holes created within the process of stitching. 
Without holes, no moisture can enter the garment, and instead, it sits on the surface before beading off. 

This beading process aids breathable membranes such as GORE-tex as it keeps water from clogging the pore based construction.

DWR is a chemical spray which is created using fluoropolymers or silicone. Working like a Teflon which is typically used on items that need a non stick surface such as frying pans,  these polymers allow water to bead straight off as a water droplet. 

DWR effectiveness can vary from brand to brand, dependent on the amount of chemical used and the thickness of the application.

Some DWR coatings can enable the jacket to be waterproof, some can only offer water repellency. Always check before you buy. 

The Lifespan of DWR

DWR eventually wears down due to use, and general oil and environmental factors cause it to break down. Washing can also remove the DWR coating, and even when using the specific care instructions for a DWR treated garment, it may last just 100 washes. 

This is the point wear many wearers of a membrane such as GORE-Tex or e-Vent feel that their waterproof is just not working, when in actual fact the pores cannot breathe. This causes the garment that was once water repelling to hold onto water, like a sponge. Condensation may form from vapours being stuck in the garment, which then gives the illusion of leaking water. Many people presume this is a leaking jacket, when in fact the breathability has been hindered. 


It is at this point that reproofing is necessary. The good news is that this is cheap and easy to do. It is also a much cheaper alternative to buying a new waterproof garment if oils or moisture have built up, your garment will still be able to be repaired.

 

DWR Reproofing At Home

To retreat a DWR Coated product, simply wash it and then apply a special reproofer, which can be a wash in or spray in water repellent. 

Normal detergents can adversely affect the Durable Water Repellent (DWR) finish and leave a hydrophilic residue, so they should never be used. 

DWR fabrics can be washed with Nikwax Polarproof which provides a DWR finish for soft garments such as fleeces, or with Granger’s Extreme Wash-In which is a water based product containing flouro-chemicals. This is the GO Outdoors recommended product for applying to most DWR coated products. 

 These coatings should be applied ‘little and often’ after the initial breakdown of the DWR coating. 

After the treatment has been applied, apply your garment to a heat source, such as an iron, tumble dryer or a radiator, which will encourage the activation of the water repellent properties. (This should be on a low setting so as to not harm the fibres and cause further abrasion to the garment. ) 

By reproofing little and often and applying heat as instructed,  your DWR treated garment should retain it’s water repelling properties season after season. 

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