Know your gear

Comfortable and dry on trek and trail

February 2008

As more and more people participate in activities that keep them on the road or veld for many hours — whether on foot or on a bicycle — the demand for garments that can protect them against unexpected rain, yet do not interfere with performance, will keep on growing.

No longer is it mainly the elite climber, intrepid expedition adventurer or overseas wintersport enthusiast who will be looking for technical garments that keep them dry on the inside as well as outside.

A different kind of customer is now asking for waterproof breatheable gear: the adventure racer or trail runner who does not like to get wet, but need to keep his or her body temperature regulated; cyclists, road and off-road runners who are out training in good or foul weather; hikers, hunters and holiday tourists who work up a sweat while on the go, but want protection from the rain.

While there are hundreds of raincoats or rain jackets on the market, they are not necessarily suitable for wear during strenuous activity.

A human expells about 4l of moisture per day — depending on the level of activity. "To have a waterproof garment with no or limited breatheability will mean that the user ends up being as wet inside (from perspiration) as if the garment wasn’t waterproof," says Ian Little of Capestorm. "Therefore, all our waterproof jackets have a high level of breatheability making them ideal for walking, trekking, adventure racing and all outdoor activities."

Customers participating in these activities are often discerning users that demand a high degree of performance from the equipment or clothing they buy. They will want to know why one garment is more expensive than the other and when they buy a waterproof breathable garment they expect it to do exactly what this description implies: allow perspiration to evaporate and keep water out. They also don’t want something that weighs them down.

How breathable or waterproof?

A black bag is the ultimate waterproof covering, a string vest the most breathable. But wearing a black bag over a string vest is not going to give you a waterproof breathable garment that will satisfy your active customer’s needs. This combo will be wetter on the inside from perspiration that can not disperse than on the outside from the rain. It will cling to the skin like clingwrap.

Put simply: you do not really want a 100% waterproof garment that traps moisture like a sauna (black bag), nor will a breathable garment (string vest) be of much use if it does not keep rain out and the perspiration from the skin.

Between these extremes are a myriad of possible combinations — some more waterproof and others more breathable. The trick is to establish what your customer needs and which product will best meet these needs. Do they want something more breathable (in which case a windproof rather than waterproof jacket might suffice) or are they more concerned about not getting wet.

How do you know what to recommend?

In an ideal world you would be able to get a chart that gives you the percentage waterproofness and breathability required for a specific activity from which you would be able to select the appropriate garment or fabric. Much like selecting the right size shoe.

But, unfortunately, even if such a chart existed, it would not necessarily give you the answer you seek.

The problem is that the tests for the breathability of fabric all give different results. Therefore, one result might look quite impressive when compared to others, while in in actual fact it is not good at all. Or one piece of fabric will come with several different test reports, depending on which tests were used (see box on next page).

Different tests were devloped in SA by the SABS, in Japan, the US, UK and Europe. The results will differ according to the methods used, laboratory conditions like temperature and humidity levels, and the kind of lamination or coating used.

And just to confuse matters even further, Gore-Tex, considered by many as the industry leader in waterproof breathability, have their own tests and standards that differ from all others.

"There are many red herrings when manufacturers announce the level of breathability of garments," says Morné Strydom, marketing manager of First Ascent. "This can lead to a lot of confusion. I suggest that a retailer ask a manufacturer which tests were conducted. A top quality manufacturer will supply test results based on different methods."

Breathability

In measuring the breathability of a garment, one laboratory would, for example, use the upright cup test, the other the inverted cup method and yet another the Ret, or Resistance to moisture vapour transmission test. (See below).

Although the format of the tests differ, they all measure the Moisture Vapour Transmission Rate (MVTR) of fabric — in other words, how many grams (or pints) of moisture will move across a square meter (or inch) of material over a 24 hour period (gr/24hrs/m2). The more moisture that moves across from the one side to the other, the better the breathability of the fabric.

As a rough guide, someone who is very active — for example, doing trail running or cycling — will produce roughly double the amount of body moisture in the same activity period as someone who is less active, for example, taking a leisurely walk.

The climate outside will also affect the MVTR: in the extreme dry air on a high mountain top, moisture would rapidly move across from the moist conditions inside to the dryness outside. But, in the extreme humidity of Durban on an overcast day, the moist air outside will leave little room for perspiration drops to disperse.

A backpack worn over a waterproof jacket will also reduce the ability of the fabric to wick moisture away and disperse it — the garment will therefore get wet on the inside where it is covered by a backpack.

Waterproof

Most outdoor retailers will be familiar with the hydrostatic head test that is conducted to measure the waterproofness of, for example, tents or backpacks. A sample of the fabric is spread over a hollow cylinder and water is then pumped into the cylinder until the water pressure is high enough to come through the fabric. The length of the column of water prior to seeping through the fabric is measured, and expressed in meters.

"The typical standard is 5-10m," says Strydom, "but again some manufacturers completely overstate the waterproofness specifications achieved through testing, even though it is not applicable for the intended use of the fabric. This can confuse consumers."

But, keeping in mind the black bag and string vest example, it is not the breathability and waterproofness individually that makes this kind of garment good (or bad), it is how they combine.

In the top end jackets worn on expeditions features like a hood that fits over a helmet but is articulated so that it swivels with your head, high reach sleeves without shoulder seams that will be damaged by a backpack and taped seams will also be important to prevent moisture entering, says Little.

Membranes

There are two ways in which a breathable fabric can be made waterproof — through coating the fabric or by applying a membrane. A membrane can either be

» microporous: minute pores allow perspiration to pass through the membrane, but are too small for drops of water to penetrate;
» hydrophillic, or water-attracting. The moisture will be attracted to the membrane and move across to the outside in a process similar to the osmosis that takes place across the membranes of body cells

Microporous membranes are not ideal for use by sailors on long sea voyages, explains Strydom, as the salt crystals become trapped in the pores and because of their jagged nature can over time agitate the pores and enlarge them to such an extent that they allow water drops through. The jacket will therefore no longer be waterproof.

The membrane is laminated to the inside of the face fabric, with dots of glue. Since glue traditionally does not breathe, the manufacturer does not want to use too much glue as this will affect the breatheability of the garment. On the other hand, too little glue will not keep the membrane properly attached. The percentage of glue coverage is usually about 15-20% of the surface.

"There are now adhesives available that are breathable, which makes it possible to apply more adhesive without sacrificing breathability," says Strydom.

Two or three ply?

Due to the fragile nature of membranes or coatings, they are usually protected by a liner, in the case of a 2-ply construction, or a scrim, in the case of a 3-ply construction. This additional layer further enhances the membrane or coating’s ability to breathe by creating a thin layer of air between the membrane/coating and the next layer, whether that is the skin or another layer of clothing.

A 3-ply construction is generally regarded as the most robust, but often also the least breathable, as a result of the additional glue required to secure the scrim.

The latest innovation is a 2.5 layer construction: 3D polymer dots on the reverse side of the membrane (like an egg tray) act like spacers to allows air circulation and protect the membrane from brushing against the skin. This means that no extra lining or mesh backing is needed, reducing weight.

Coatings

Coatings are sprayed on face fabrics with micro-jets and the excess liquid scraped away in a highly specialised process until a veneer thin layer (30 microns) remains. This application requires a high level of skill. If the coating is too thick, it will impair breathability, and if it is too thin, it will leak.

Because this is a difficult technique that not all manufacturers master with equal skill, the perception developed that membranes are superior to coatings.

"Improvements in the application and performance of coatings has, however, meant that many of the modern coaings are producing better performance results than membranes," says Strydom.

Durable water repellent (DWR)

This is a finish treatment applied to the outer material to improve waterproofing. The finish causes waterdrops to form beads that roll off the fabric, instead of water pooling on the outside of the fabric and saturating it.

This is often used in combination with a coating or membrane.

While a DWR on its own does not make the garment waterproof, it will repell sufficient water to keep the wearer dry in a light rain. It also forms a buffer between the inside and outside of the garment that helps to reduce condensation on the inside and aids in water vapour transfer.

Without the DWR — or if it no longer works — the outer surface will become saturated, which will make it feel cold due to increased condensation. This will create the impression that the jacket is leaking.

Just like a car needs to be serviced, the DWR finish needs to be refurbished when it is affected by wash, wear, or dirt. A special purpose wash restores the DWR and rejuvenates the garment face fabric.