Singing In The Rain- Watertightness of Clothing Materials By Markus Weder,EMPA (Swiss Federal Laboratories for Materials Testing and Research), St. Gallen, Switzerlan ISO BULLETIN JUNE 2001

Rain, rain, go away, come again another day, chant the children. But, no, rain is not going to go away. Indeed, according to the climate model calculations, global warming will cause increased rainfall in many regions of the Northern Hemisphere. However, ISO standards will help those that have to tolerate an excess of it to keep singing in the rain. By developing standards on tests for making rainwear as watertight as possible, and giving it breathability, the ISO standards for watertight materials are yet another way standards have of making life more comfortable in the many situations where the human being seeks to keep dry.

The author looks at the ingenious means, from a James manikin to water towers, used for testing for watertightness and breathability, that are allowing research to make progress, and how ISO standards are having a growing influence in enabling an assessment to be made of the quality of the watertightness of ready-made articles of clothing under nearreal-life conditions.

Watertightness of Clothing Materials

The standards for watertight-ness are used on one hand by fabric manufacturers and on the other by garment manufacturers. Present-day national standards frequently specify the use of simple test methods (e.g.ISO 811, Textile fabrics Determination of resistance to water penetration Hydrostatic pressure test) for the assessment of the watertightness of clothing materials. ISO 811 is relatively simple to use and based on static pressure measurements, which do not correspond to the dynamics of a shower of rain in practice. The CEN/TC 162 WG 4 PG1 standard foreseen,a standard for a rain tower, will, in particular, be used for workwear and protective clothing (military, firefighters, police, railway workers, etc.) and will help to recognize mistakes in the making at an early stage, and, in general to improve the quality of ready- made garments. Future standards will also have to consider aspects of durability, which means that the quality of watertightness has to be assessed after controlled, simulated use.

Come Rain, Come High Water

Rain is not constant in practice and, depending on the situation, its intensity varies enormously. A drizzle, for example, is far less intensive than a cloudburst, and the period of time during which a rainwear article is exposed to rain also plays an important role. This disparity needs to be overcome with the development of a rain tower test.

As its name implies, the job of rainwear is to protect the body primarily against external moisture or precipitation. However, many materials are available these days that not only claim to be rainproof, but also to expel moisture resulting from intense physical activity, and to propel it out. Given the difficulty of this balancing act between protection and physiology, a product often does not come up to expectations. In the last few years, so-called breathable rainwear has also been used as industrial clothing. The experience gained has not always been positive and one may justifiably ask why. As fabrics, breathable rain-protection materials are usually waterproof. However, as soon as articles of clothing are made from them, e.g., rain-protecting jackets or trousers, the weak points soon become apparent. In principle, the most dreaded places are the seams as a whole, the exposed seams on the collar and shoulders in particular, as well as zip fasteners and ventilation openings. Moreover, the sucking effects of the seam or arms, or manufacturing errors can also cause leaks. Though difficult, it is still possible, however, to manufacture excellent products which, in a state as new can also withstand a prolonged cloudburst in the rain tower.

In real-life use, depending on the application, rain-protection products are subjected to enormous loads. Leaks occur frequently, particularly in clothes used in the building industry or during military service. So that the priority here also is for watertightness, good breathing properties and durability.

The role of the EMPA

The EMPA (Swiss Federal Laboratories for Materials Testing and Research) is actively involved in both national and international research, and participates in various different ISO, CEN, ASTM and Swiss national committees. Such norms serve to standardize test procedures. Results from differing test institutes are only truly comparable under the same experimental conditions. Standards should not only be developed to be easy to use but also, much more importantly, to be relevant to the demands in practice. As an impartial research institute, EMPA provides the scientific basis and the technical knowledge for standardisation work to assist Swiss trade and industry in maintaining and improving its market position.

Watertightness

How is the watertightness of rain-protection materials defined and measured? When can we say that a material is really rainproof?

In general, this property is proven and assessed with the hydrostatic pressure (water column) method according to ISO 811,Textile fabrics Determination of resistance to water penetration Hydrostatic pressure test. In view of its simple application and good reproducibility, this method is extremely popular. Nevertheless, it does raise some critical questions when it is considered more closely. Is it justifiable to select a method merely on the basis of its good

reproducibility and relatively simple application? How does this method work in practice and how relevant are the results to actual use?

According to ISO 811, materials with a hydrostatic head of more than150 cm can be designated, in general, as rainproof. In the advertising field, however, the manufacturers of rain-protection materials outbid each other with hydrostatic heads of 80 m and more. But the materials are stressed with a static water pressure of only 2-3 mm in use. Rain is a dynamic and not a static process.

As fabrics, breathable rain-protection materials are usually waterproof. However, as soon as articles of clothing are made from the, e.g., rain-protecting jackets or trousers, the weak points soon become apparent.

All these questions and problems induced EMPA to take a closer look at the subjects of rain- and watertightness. This soon led them to the conclusion that new, more practice-related test methods were necessary. During the past years, various new models have been developed and applied to test and assess the rain- and watertightness of materials and ready-made garments. These test methods and the results of numerous measurements are described and discussed in this article.

The watertightness of fabrics can be tested in various ways:

• Hydrostatic head (EN 20811) • Bundesmann (EN 29865) • Milling/Squeezing Test (Elbow effect) • Centrifugal test (Watertightness under the influence of wind) • Pin-penetration with the Bundesmann test • Bundesmann according to the pin-penetration test

Watertightness under mechanical stress (Milling/Squeezing Test)

Parts of the body like the elbow, knee or shoulders are sometimes subject to mechanical stress when a rucksack is carried on the back. This has a direct influence on the watertightness of a material. The milling/squeezing test apparatus, with which the penetration of water under mechanical pressure can be measured, was developed to determine this effect metrologically.

Rain test with high impact velocity of the water drops (up to 145 km/h)

There are numerous applications where raindrops are projected onto a garment at a high velocity, e.g. by motor cycling or strong winds. These are highly dynamic processes and have to be considered differently. A new apparatus (see Figure 1) has been developed in which a sample is mounted on a moving arm turning at a peripheral speed that can be varied to anywhere between 0 and 145

km/h. This apparatus is placed in the rain tower and subjected to rainfall from a height of over 10 m. The water penetrating the sample is absorbed by blotting paper, which is weighed prior to and after the test.

The Bundesmann pin-penetration test

With this test, 17 pins (Type 110/18) are pressed through a sample with a diameter of 13 cm at a defined speed of 1000 mm/ min. Watertightness is tested according to Bundesmann prior to and after the penetration of the pin. The reduction in watertightness as a result of the defined damage is a dimension for the receptive type¬ù of the material as concerns damage. The next stage of the test can be performed once the fabric is in order again.

The measurement of watertightness by high velocity impingement.

This apparatus is designed especially for the testing of motor-cycle clothing, cycling apparel or mountaineering clothing. Materials, which have a hydrostatic head of more than 20 metres, can already suffer damage through being subjected to rain- drops having a velocity of 65 km/h, with the result they are no longer watertight. On the other hand, materials have been tested with a hydrostatic head of 30 cm, which remained absolutely watertight when they were subjected to velocities of more than 130 km/h in this test. With certain types of material, there is a tendency towards increased water penetration at higher velocities of projection, even though the material remains intact.

Rain test on ready-made jackets (Rain tower test with James).

Several European test institutes are already working with a rain tower¬ù. Larger companies as well as military institutions employ rain towers. Their operators have now joined forces and developed a draft norm in CEN/TC 162 WG4 PG1, which is now in the initial inquiry stage.

James is a test method for determining the watertightness of a ready-made jacket. An anatomically formed and jointed manikin (height 1,8 m) is dressed in the jackets to be tested and subjected to artificial rain in a rain tower. Twenty-two conductivity sensors are arranged over the upper extremity of the of the manikin. The system is exposed to rain for a specified time and the conductivity sensors register where and when water penetrates inside the jacket.

A cotton vest is put on the manikin underneath the jacket. The water absorbed by the vest changes the electrical conduction, and is registered as water penetration by the sensors. Furthermore, on completion of the measurement (i.e., normally after rain for one hour), the wet area of the vest is assessed visually. The jacket is then rated from 1 to 5, depending on the size of the wet area. Three jackets per type are measured, and the mean value of the wet area indicated so that the result is not only valid for the measured jacket, but will also enable a number of

conclusions to be drawn for each respective type. Any visible damage is noted explicitly in the test report. It is not expedient to test only one jacket per sample type. In principle, at least three jackets should be tested to obtain reasonable statistical and conclusive evidence. If only one of the jackets leaks, it is possible that it has suffered damage during transport, and can tell us very little about its quality. three tested jackets leak, it must be assumed that the quality of the jacket is imperfect and has to be improved.

Up to now, the weather-protection clothing on James was subjected to a cloud burst of rain: 2000 drop-former shower of rain equal to 450 l/m 2h over an area of 2 m 2. The raindrops fall onto the sample from a height of 10 m, and correspond in quantity and drop size (diameter about 5 mm) to those of the Bundesmann rain shower test according to EN 29865. However, in contrast to the Bundesmann test with real life. The velocity of the drops in real weather depends on their diameter, at about 2 to 9 m/s. The drops created in the rain tower correspond to the upper limit. Only tests using the manikin provide information as to whether the selected material is sufficiently watertight. The tests in the rain tower have revealed the most frequent weak points of jackets.

• Seams (collar seams, hood attachment seam, zip-fastener seam) • Ventilation openings • Sucking effort by way of seams/sleeve ends (water-repellency treatment) • Draw-strings • Pockets • Hood • Absence of rain seam by the front zip fastener

The intensity of the rain and the time factor, i.e. how long a person can remain outdoors by a specific rain intensity, have a decisive influence on the choice of the rain protection material for a particular activity.

Breathability of clothing

Nowadays, breathability is frequently measured by means of a Cup method (ASTM E 96 E, DIN 53122, ISO/WD 15496) or with the skin model according to ISO 11092, Textiles Physiological effects Measurement of thermal and water- vapour resistance under steady- state conditions (sweating guarded-hotplate test). In terms of quality control, there is nothing wrong in using these methods. So- called breathability is not the sole or the decisive factor as concerns the comfort of a clothing system. If we are concerned with actual use, however, we should look as in the case of watertightness to test methods, which allow a statement to be made about manufacture of articles of clothing.

The vaporization of perspiration can retard an excessive increase in body temperature. What is important, however, is where the sweat evaporates.

With light physical activity, the moisture produced by the body evaporates in the perspiratory glands, and is eliminated more or less as water vapour through the first layers of clothing. At lower temperatures, part of this water vapour condenses in the outer layers of clothing. In the case of intense physical activity, the wearer will inevitably perspire mainly in the form of moisture to dissipate the large quantity of heat (up to about 700 W) efficiently. The vaporization of perspiration can retard an excessive increase in body temperature. What is important, however, is where the sweat evaporates. If it evaporates close to the skin in the underwear, it extracts far more energy from the body than when the sweat is transported in a wet state to the next layer and evaporates from there. The question as to whether the former or the latter is desired depends on the respective application.

In the case of winter clothing, where there is normally a lack of warmth, the wet moisture should extract as little energy as possible during short-term physical activities. It should be transported quickly in a wet state to the next layers, because the body will be at rest again within a few minutes, and should not be cooled any further at this stage. In case of activities in more moderate climates, e.g. when walking in an ambient temperature of 15', the wet sweat secreted by the body should be transformed efficiently into cooling energy. The better the evaporation cooling, the less the body has to perspire and thus the more efficient it is. The so-called post exercise chill¬ù is a very important factor, i.e., the moisture remaining in the clothing after a physical effort continues to cool the body until that moisture is transported away from the layers close to the skin.

Cotton, for example, has a long post-chilling effect, because the moisture absorbed evaporates only slowly. Polyester, on the other hand, has a relatively short cooling time, and is therefore better for use in sweat-producing activities than cotton.

Whereas only absolutely watertight and water-vapour- tight coatings were used in the past, breathable materials are employed very often nowadays. In case of very strenuous physical activities, a relatively large quantity of wet sweat has to be exuded in order to cool the body sufficiently.

The transport of heat and moisture in practice is very complex, and can actually only be investigated using methods that exhibit boundary conditions similar to those in actual use. During the last ten years, EMPA has developed new methods for testing the simultaneous transport of heat and moisture in clothing materials.

Satisfying comfort of wear, however, does not depend necessarily on the rapid expulsion of all the moisture. Depending on the situation, intermediate storage in layers away from the skin, for example, can also be sufficient (as for shooting jackets or NBC suits).

Wet-protection clothing

The fields of application have changed considerably since the emergence of water and wind-proof breathable rain-protection materials. Whereas only absolutely watertight and also water-vapour tight coatings were used in the past, breathable materials are employed very often nowadays.

The so-called highly breathable coatings or special fabrics are used if the particular field of application does not call for 100% watertightness.

These materials have an even thinner coating than those used for the customary laminates, and the seams are frequently and intentionally not sealed. In case of very strenuous physical activities, a relatively large quantity of wet sweat has to be exuded in order to cool the body sufficiently. A certain feeling or wetness will be sensed nevertheless, because of the resulting quantity of moisture, but here protection against overheating is more important than the feeling of wetness.

Water-repellent materials are equally suitable for numerous applications. The difficulty by the selection of rain-protection materials for the industrial clothing sector is the determination of the respective requirements. One has to provide not only expediently adapted protection against the weather, but also account for the necessary minimum breathability.

To be on the safe side, the best weather protection and the highest breathability are frequently required. However, the fact that one has to pay dearly for all these positive characteristics is frequently over-looked.

The so-called highly breathable coatings or special fabrics are used if the particular field of application does not call for 100% water- tightness.

The lotus leaf ideal

The protection against wind and weather, even with used materials, takes priority over good breathability. It is not much help to the wearer if he has agreeable wear-comfort in dry weather, but always gets wet when it rains.

In principle, a rain-protection jacket should have very good and long-lasting hydrophobing, very few seams and be washed as little as possible.

In addition to watertightness, breathability also plays an important role. Here again, the tests need to be conducted as near as possible to real-life conditions. It is with this in mind that the Manikin Family at EMPA in the last few years has grown, and the three James manikins, used for watertightness assessment in the rain tower, have been joined by others, such as Alex on whom headwear can be

investigated, and Henry, used for heat-protection tests. The latest development SAM¬ù (Sweating Articulated Manikin) will be completed this summer. It has been developed over a period of four years, and will be used for the initial investigation of physiological tests and research activities in near real-life conditions.

The aim to obtain a permanent water-repellency, as good, for instance, as that of a lotus leaf, is very ambitious and extremely difficult to realize. Further intensive efforts need to be made in the future to ensure that high-quality rain-protec-tion materials remain tight even after more protracted use or, as concerns watertightness, to lend them a certain resistance to damage. This might be done, for example, by means of a further water barrier or so-called intelligent textiles, which can adapt their function according to changing boundary conditions. One of the most frequent sources of error is the sucking effect inside a jacket. Good hydrophobicity enhances the tolerance towards possible damage considerably.

New international standards for the testing of ready-made garments for watertightness under the most realistic conditions possible play an important role in enabling us to guarantee the best possible quality and to generate customer satisfaction.