MERINO FOR PERFORMANCE ACTIVEWEAR

MERINO FOR PERFORMANCE ACTIVEWEARUsage of Merino active wear is growing rapidly, worldwide, supported by strong consumer endorsement and objective evidence of performance. Merino apparel and hosiery offers a means of enhancing wearer physical performance and comfort when engaged in physical activity, and avoids the use of non-sustainable synthetic fibres.

WHAT PERFORMANCE CHARACTERISTICS ARE IMPORTANT IN ACTIVEWEAR?In addition to normal textile characteristics, the following attributes are particularly important for fabrics utilised in active wear.

• Anabilitytoactivelymanageheatandmoistureflowsfrom the body under a variety of conditions (hot, cold, dry and wet)

• Suppressionofodour

• Highabrasionresistanceanddurability

• Easeoflaundering

• Softnessandflexibility

WHY IS THE ABILITY TO MANAGE HEAT AND MOISTURE FLOWS IMPORTANT IN ACTIVEWEAR?Theabilitytomanageheatandmoistureflowshasamajorinfluenceonthethermalstateofthebody,onhumanperformance and on a users’ perceptions of their physical condition.

With respect to thermal comfort, the required attributes of fabric differ greatly depending on the intended end use. By way of example, sedentary activity in a cold environment will require fabric insulation and moisture transfer requirements quite different to those required of a garment designed for sporting use in a warm or temperate climate. Generally, active wear fabrics are designed to promote heat and moistureflowsawayfromthebody.

Howfabricsregulateheatandmoistureflowsareintrinsically linked. To illustrate this, consider the case of active sportswear. Such apparel should ideally support the thermoregulation of the athlete by promoting evaporative heat transmission (Pessenhofer et al. 1991). Such heat transmission arises through conversion of liquid sweat to water vapour at the skin surface, the efficiency of which is dependent upon the temperature of the skin and surrounding air, the relative humidity of the air on either side of the fabric, air interchange from under the fabric, and the ability of the fabric to pass water through it in vapour form. The latter is mediated by fabric, but driven by concentration gradients existing between the environment above the skin surface and that exterior to the garment. Failing to promote such dissipation will lead to a rise in core body temperature and contribute to cessation of physical activity through exhaustion.

Three principle modes of moisture (either liquid or vapour) flowinMerinotextilesexist(MassieandMehta,1980).

• Watervapourtransportthroughfibres(byabsorption/desorption).

• Watervapourtransportthroughairspacesinthefabricstructure.

• Liquidwatertransportthroughfabrics(alongfibresurfaces via capillary action).

HOW DO MERINO FIBRES TRANSPORT WATER VAPOUR THROUGH THEIR STRUCTURE?Water vapour absorption is an intrinsic fibre quality and hence independent of fabric structure (Massie and Mehta, 1980).Woolisabletoactivelyabsorbmoisturefromtheatmosphereand/orbody–withitsabsorptionpropertiesbeing much greater than most synthetic fibres (Figure 1).

Figure 1. Moisture absorbance of wool and synthetic fibres (Collie and Johnson,1998).

Wool owes its absorption characteristics to its chemical building blocks, amino acids, which are hydrophilic. This means they attract and absorb water molecules, with such water becoming associated with the amorphous regions of the intercellular cement and the fibre matrix. This interaction with water occurs in a rather special manner.

Firstly, as the hydrogen bonds that bind the water molecules are reversible, water can also be released in a process known as desorption. Secondly, a wool fibre will absorb up to 35% of its own weight in water at a high humidity, before feelingwet(Leeder1984;CollieandJohnson1998).Incomparison, most man-made fibres are able to absorb less than 5% of their weight in moisture at the same humidity (Leeder1984).

In addition to these moisture absorption properties, wool has an important differentiator in apparel usage in that an appreciable quantity of heat is also generated as water is absorbedintothefibre(Figure2);andthenlostagainasthegarmentdries(Leeder1984)–effectivelywarmingandcooling the wearer when needed the most.

Figure 2. Heat of sorption of wool and other synthetic fibres (Collie and Johnson,1998).

This energy release is referred to as ‘heat of sorption’ and occurs in all fibres to some extent, but is particularly pronounced in wool. The extent to which the processes of absorption and desorption occur is governed by the relative humidity of the surrounding environment and existing moisture content of the fibre. The higher the ambient humidity,thegreatertheabsorptionofwater(Leeder1984).The reason Merino gives off heat when it absorbs water as either liquid or vapour relates to:

• watervapourcondensingwithinthefibre(releasingitslatent heat of condensation)

• waterdisruptingexistingbondingnetworksandstructure within the fibre, forming new chemical bonds (with an associated energy release).

Put simply, addition of a polar molecule like water alters the internal chemistry of Merino to release energy as heat. Conversely, removing water (eg. by drying) requires the opposite–aninputofenergy.

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These moisture absorption and desorption characteristics provide additional important functional characteristics to wool garments. For example:

• Whenawoolfabricexperiencesasuddenchangein the environment associated with its wearer, such as increased activity leading to sweating, wool acts as a buffer, absorbing the extra moisture quickly and dissipatingitgradually(Leeder1984).Thesameoccursfor the external environment, where wool acts as a buffer to changes in atmospheric humidity (Onions 1962). As a result, wool can prevent the ‘clamminess’ that can occur in environments of high humidity (Collie and Johnson, 1998).Supportingthis,studieshaveshownthatwoolfabrics still provide a similar level of performance as polypropylene or nylon fabrics of a similar construction with respect to perceived comfort, skin temperature and core body temperature (Rodwell et al. 1965, Rodahl etal.1973,Holmer1985,BakkevigandNielsen1994)(BakkevigandNielsen1994),despitewooltcontaininggreater levels of moisture. This benefit is most likely conferred because of the energy released (heat of sorption) when wool absorbs that moisture.

• Incoldclimates,wheretherelativehumidityindoorsin winter is generally lower than outdoors, wool garments conditioned (equilibrated) in a dry indoor environment immediately begin producing heat when taken outdoors, buffering the wearer against the sudden temperature drop they experience. On exposure to a saturated atmosphere, the heat produced by a kilogram ofdrywoolasittakesup35%watervapourisabout960kJ, equivalent to the heat output from an electric blanket over8hours.Thiseffectoccursquitequickly,typicallyin the first 2-5 minutes and then decreases until the moisture content of the wool reaches equilibrium with the higher relative humidity of the atmosphere.

HOW DO MERINO FABRICS TRANSPORT WATER VAPOUR THROUGH THEIR STRUCTURE?Just as the ability of individual fibres to absorb water in vapour form is important, a fabric’s ability to allow water vapour to pass through it is also critical to managing body temperature and maintaining comfort - especially when the wearer is participating in athletic activity.

The importance of this becomes apparent if one considers thatunderrestingconditionsthebodymaylose0.5litresof water through perspiration each day, however during strenuous exercise this can increase to up to 1 litre per hour. If transmission of moisture (in vapour or liquid form) is impeded, it can build up against the skin, creating wetness or clamminess for the wearer.

Becausewoolfabricsareporous/lofty/bulkyandnotcompletely impermeable to air, they also provide an avenue for moisture transmission through air spaces between the fibres and yarns. Such water vapour dispersion can be further enhanced by movement of the wearer, which causes a ‘pumping’ of air close to the skin through to the outside of the garment, both through the fabric itself and throughopeningsatcollars,sleeves,etc(Leeder1984).In this respect, design and fit of the garment are also very important.

HOW DO MERINO FABRICS TRANSPORT LIQUID MOISTURE THROUGH THEIR STRUCTURE?The interior of the wool fibre has a greater affinity for water than the exterior of the fibre, but both have the capacity to transport water in one form or another. The degree of water repellence of a fibre is determined by its surface energy, with higher surface energies found in fibres that are more easily wetted and promote the wicking of water along their surfaces. Polyester, acrylic and nylon all have higher surface energyvaluesthanwool(Leeder1984),butalesserultimatecapacity for moisture (Figure 3). Polypropylene has a similar surface energy to wool and (all other things being equal) could be expected to have similar wicking properties to wool.

Figure 3.Fibresurfaceenergiesofvariousfibres(Leeder,1984).

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Having said this, it is important to remember that the moisture management characteristics of wool arise through different mechanisms to those seen in synthetic fibres. Typically, synthetic fibres rely solely on liquid water transport fortheirwatermanagementcharacteristics–thisbeingdictated by the cross sectional shape of the fibre (eg hollow, solid, round, trilobal, etc) and surface characteristics (which govern how easily liquid will travel along the fibre surface). Whilst wool also has the potential to ‘wick’ water in this way, its superior moisture management characteristics arise becauseofitscapacitytoalsoabsorb/desorbwatervapour–aprocessthatstavesofftheneedtowickliquidwateraway(Leeder1984).

Irrespective of the mechanisms of moisture transport through textile structures, those made of wool have been shownbyHolmer(1985)toabsorbmoreliquidthanthoseofnylon(245gvs198gofsweat)orpolyester(Lietal1992).

WHAT DETERMINES HOW WARM A GARMENT FEELS?The skin has nerve endings that will detect even minute or brief temperature changes, and the degree of coolness or warmth felt by the wearer will depend on how well fabric conducts heat away from the skin. Heat has a natural tendency to move from warmer to cooler regions, and losses by the human body occur in a number of different ways:

• Radiation

• Conduction

• Convection

• Evaporativecooling

Radiation is the primary mechanism by which the body emits and absorbs heat, with up to half of body heat loss occurring through this means. Heat also transfers from the body to objects, via conduction, because the temperature of clothing fabrics is typically between that of the environment and that of the skin. Because warm air is lighter than cold air, it rises and is replaced by cooler air, with the resulting convection currents also carrying heat away from the body. Finally, evaporative cooling (of sweat) also allows the body to dissipate excess heat. Conduction andconvectionaccountfor15-20%ofheatlosstotheenvironment.

The thermal resistivity (R) of a fabric is a measure of its insulatingproperties–andhenceofitsrelativewarmth.Thermalresistivityisinfluencedbyarangeoffactors,butthekey ones are:

• Thefabricsurface;

• Thefibrescontainedinthefabric;and,

• Theairtrappedinthefabric,yarnorinthe fibres themselves.

To summarise, when the environment temperature exceeds skin temperature, the body will gain heat through radiation and conduction and only lose heat through evaporative cooling. When the environment temperature is lower than skin temperature, the body will lose heat to the environment through radiation, conduction, convection and, if active, through sweat evaporation.

HOW DOES MERINO APPAREL PERFORM IN TERMS OF THERMAL RESISTANCE AND WARMTH?The key parameter determining the thermal resistance of a fabric is the amount of air it traps in its interior - which is stronglycorrelatedwithitsthickness(Figure4).Fibretypeisonlyofsecondorderimportance(PierceandRees1946,HolcombeandHoschke1983),althoughwooldoeshavesome advantages over other fibres in this respect. Due to the crimp of the fibres, wool fabrics have an inherent bulkinessorloftasthefibresareunabletopacktogethertoo closely in the yarn structure. The resilience or elastic recovery of the wool fibre allows this bulkiness to be maintainedovertime(Leeder1984).

Figure 2.Influenceoffibretypeandfabricthicknessonthermalresistanceof underwear.

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Air permeability has been found to increase as mean fibre diameterincreases(vanderMerweandGee1985)andMerino garments are able to be manufactured in a variety of thicknesses, structures and micron ranges in order to tailor the insulative effect to the intended end use.

Illustrating this, heat transmission or dispersal can be assessed by measuring fabric surface temperature (Figure 5). In a study by Pessenhofer et al. (1991), fabric surface temperatures were higher for wool, indicating improved heat dispersal characteristics, while measures of retained heat were significantly lower for wool than for polypropylene.

Figure5.Infra-redimagetakenofathleteafter30minutesofexercisewearing garment comprised half of merino (RHS of image, as viewed) and halfofpolyester(LHSofimage)–showinghighersurfacetemperatureswith the merino half, indicative of more efficient heat release.

When assessed subjectively, subjects involved in the investigation gave more positive responses to garment comfort questions with respect to wool than they did for polypropylene (Pessenhofer et al. 1991). Achievement of higher levels of stress by athletes in wool garments than by those in polypropylene garments indicates that aerobic performance capacity, that is the supply of energy through the oxidation of nutrients, is available to a greater extent in the wool clothing. This can be important in sporting competition, where only slight differences in time and performance can be extremely important in terms of outcomes (Pessenhofer et al. 1991). Wool also exhibitsfavourabledynamicadaptationtotheflowofheat from the athlete to the environment. This is possibly due to the loading of the fibre with moisture from the massive generation of sweat that takes place following the commencement of high-load activity (Pessenhofer et al. 1991).

WHAT OTHER IMPROVEMENTS IN PHYSICAL PERFORMANCE RESULT FROM WEARING MERINO?In addition to the examples cited above, a study (Laing et al2007)comparingphysiologicalresponsesofathletesexercising while wearing single layers of Merino, polyester or50/50Merino/polyesteractivewear(237±16g/m2),underhot and cold conditions, revealed the following statistically significant differences

• Alongertimetoonsetofsweatingwhilstwearingmerino single jersey fabric (Figure 6).

• Lowerheartrateduringrestingandwalkingwhilstwearing Merino in hot conditions (Figure 7).

• Lowerheartrateduringrunningandwalkingwhilewearing Merino in cold conditions.

• Greaterheatcontentofthebodywhenwearingpolyester interlock fabric (under both hot and cold conditions).

• GreaterstabilityofskintemperatureunderMerinofabric.

• Greaterstabilityincoretemperaturewhilstrunning,walking and resting in Merino (hot and cold conditions)

The performance of garments constructed from 50/50Merino/polyesterfabricexhibitedperformancecharacteristics intermediate to those made from either 100%Merinoor100%polyester.

Figure 6. Time to onset of sweating when exercising wearing merino vs

polyester base layer product.

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Figure 7. Change in heart rate when exercising wearing merino vs polyester base layer product.

HOW DOES MERINO SUPRESS BODY ODOUR COMPARED WITH OTHER FIBRES?Another key consideration with active apparel is its propensity to build up unwanted body odours. Body odour arises as the result of the build-up of bacteria and micro organismsontheskinand/orinwornapparel/hosiery.Oneof the key contributing factors to the build-up of bacteria and body odour is sweat on the skin surface. The human bodyhasmorethan3,000,000sweatglands,whichcontinuously secrete moisture. Sweat by itself does not have any odour. However, if sweat remains on the skin for a period of time, bacteria are likely to proliferate, creating the body odour that many find offensive. Such body odour is due largely to volatile fatty acids produced by these bacteria as a waste product.

Apparel fabrics constructed from Merino fibre have been found(McQueenetal2007a,b)toexhibitasignificantlylowerpropensityforodouremissionafterwearthanpolyester fabrics of a similar weight and construction (Figure8).

Figure 8. Propensity for odour emission by fabrics of similar construction (SEMs indicated).

Further supporting this, a study carried out by researchers at the of (WRONZ), who used a panel of human noses to comparetheeffectofdifferentfibretypesonodour–askingeach participant to rank the odour of used socks in a series ofpairwisecomparisons(Burling-Claridge1998).Theresearch found that the odour generated on wool socks in active use was significantly less objectionable than that of other fibres (Figure 9).

Figure 9. Propensity for odour emission from socks constructed of differing

fibres(Burling-Claridge1998).

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HOW DOES MERINO APPAREL PROTECT FROM ULTRAVIOLET RADIATION?Ultraviolet (UV) radiation is a component of the solar radiation that comes from our sun and to which many people are exposed whilst engaged in active pursuits. Overexposure to UV radiation can have harmful effects on human health, ranging from moderate sunburn, through to melanoma. The potential for a fabric to protect its wearer from ultraviolet radiation is described as its Solar Protection Factor (SPF) or, more commonly, its Ultraviolet Protection Factor (UPF). UPF relates to the time taken before human skinbeginstoreddenafterexposuretoultravioletlight–andisusuallymeasuredonascaleof0-50.Untilrecentlythere was a widespread perception that clothing afforded complete protection against such radiation, however, there is an increasing understanding that this may not necessarily be the case. Some fabric constructions perform much better than others, as do some fibre types.

Manyfactorsinfluencethelevelofultravioletprotectionagarment provides. When radiation strikes a textile surface somecomponentsarereflected,someareabsorbed,andsome pass through it. The greater the amount of radiation able to pass through the textile, the lower the UPF. The most importantofthefactorsinfluencingUPFaresummarisedbelow:

• Fibretype(withtheUPFbeingdictatedbysuchthingsas chemical composition, ecru colour, fibre cross sectional shape, presence of delustrants, etc). Wool typically has a much higher UPF than synthetic fibres such as polyester.

• Fabricdensity(withdenserknit/weavestructuresconferring a higher UPF).

• Degreeofstretch(withtheUPFbeingloweredinastretched state).

• Fabriccolour(withtheUPFfactorconferredbeingdependent upon the amount of dyestuff present and the chemistryofthedyeitself–notingthatdarkercoloursusually, but by no means always, result in a higher level of protection being conferred).

• Whetherthefabriciswetordry(withtheUPFdecreasing markedly when wet).

• PresenceofUVabsorbingfinishesand/oropticalbrightening agents (with a range of proprietary finishes able to be applied to fabrics in order to increase the UPF).

• Garmentdesign

Merino wool affords excellent UV protection. Research by Hilfikeretal(1996),Reinertetal(1997)andHaerri(2000)has shown that wool absorbs radiation throughout the entire UV spectrum, whereas untreated cotton, nylon, acrylic, and silk are poor absorbers of UV. Polyester absorbs UV predominantlyatlowwavelengths–butwithlittlebenefitasthese are the same wavelengths that the earth’s atmosphere is also efficient at screening out.

InastudybyGamblicheretal(2001)morethanhalfof236 fabrics surveyed fell below the European standard for ultravioletprotectionofUPF>30.All100oftheMerinofabrics passed the test, with even the worst performing fabricstillhavingaUPFgreaterthan40(Table1).Incontrast,allofthelinensamples,and89%oftheviscosesamplestestedfellbelowthestandardofUPF30–whilethe other fabrics tested (nylon, polyester, cotton and blends thereof) fared equally badly. For example 79% of the cotton fabricshadaUPF≤20.

Table 1.UPFFactorfor236Summerfabrics(meanweight158g/m2).

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Wool - - - - 27 73

Cotton 28 28 21 - 7 14

Linen 31 52 20 - - -

Viscose 52 29 9 6 2 1

Polyester 2 4 2 2 11 22

Nylon 44 19 - - - 38

Blends - 10 12 14 19 46

KEY POINTSHeat and Moisture Management

• Merinofibrehasahydrophobic(waterrepelling)exteriorand hydrophilic (water loving) interior that confer its unique moisture management properties , resulting in enhanced wearer comfort and performance.

• Incontrasttomostsyntheticfibres,woolhasthecapacity to remove large amounts (up to 35% of its own weight) of moisture from the skin surface, before the fibre even begins to feel wet.

• Afabric’sabilitytoallowthetransmissionofwatervapour through its structure will significantly affect the comfort of the wearer. The ability of Merino fabrics to do this surpasses that of synthetics.

• ThechemicalstructureofMerinofibremeansthatithas the ability to absorb and desorb moisture and to gain and release heat depending on the external and internal environment - thus buffering wearers against environmental changes.

• Asitabsorbsmoisture,Merinofibrereleasesasmallbut perceptible amount of heat. In an apparel or hosiery application this prevents the wearer from chilling in wet, cool conditions. In hot conditions the reverse effect occurs, affording a natural means of buffering the body’s microclimate.

Odour Supression/Ease of care

• Bodyodourarisesasaby-productofbacteria,whichproliferate in warm moist environments (e.g, when sweat is allowed to remain on the skin for a period of time).

• Merinofibre,throughitscomplexchemicalandphysicalstructure, resists the development and proliferation of odour to a much greater extent than synthetic materials or cotton.

• Merinoapparelandhosieryisreadilylaunderedtoremove soil or other contaminants of potential relevance to health - and efficient shrink resist processes are employed to enable full machine washability.

UV Protection

• UVradiationreachingearthfromthesuncanhavedeleterious effects on human health when overexposure occurs.

• Merinofibreisaveryefficientabsorberofpotentiallyharmful UV-A and UV-B radiation.

• Fabricconstructionisalsoakeydeterminantoftheextent to which textiles will protect a wearer from UV radiation.

• Summer-weight Merino garments have been consistently shown to offer a higher degree of UV protection than fabrics constructed of competing materials.

REFERENCES

Bakkevig,M.KandNielsen,R.1994.Impactofwetunderwearonthermoregulatory responses and thermal comfort in the cold. Ergonomics, 37,1375-89.

Burling-Claridge,G.R.,1998.Odourproductioninactivesportwear.WRONZ Confidential report.

Collie,S.R.andN.A.G.Johnson,1998.Thebenefitsofwearingwoolrather than man-made fibre garments. Lincoln, Christchurch, New Zealand, WRONZ.

Gambichler,T.,Rotterdam,S.,Altmeyer,P.,andHoffmann,K.,2001.Protection against ultraviolet radiation by commercial summer clothing: need for standardised testing and labeling, BMC Dermatology, 1: 6.

Hilfiker, R., Kaufmann, W., Reinert, G., and Schmidt, E., 1996. Textile Research Journal, 66: 2, 61.

Holcombe,B.V.,andHoschke,B.N.,1983.Dryheattransfercharacteristicsofunderwearfabrics.TextileResearchJournal,53,368-74.

Holmer,I.1985.Heatexchangeandthermalinsulationcomparedinwoollenand nylon garments during wear trials, Textile Research Journal, 55: 9, 511-8.

Laing, R. M., Sims, S. T., Wilson, C. A., Niven, B. E., and Cruthers, N. M., 2007.Differencesinwearerresponsetogarmentsforoutdooractivity.Ergonomics, 1-19.

Leeder,J.,1984.Wool-Nature’sWonderFibre,AustralasianTextilePublishers.

Li, Y., Holcombe, B. V., and Apcar, F., 1992. Moisture buffering behaviour of hygroscopic fabric during wear. Textile Research journal, 62: 11, 619-27.

Massie,D.S.andMehta,P.N.,1980.Moisturetransportpropertiesofunderwear fabrics. Ilkley, Yorkshire, UK, International Wool Secretariat, Technical Centre.

McQueen,R.H.,Laing,R.M.,Brooks,H.J.L.,andNiven,B.E.,2007a.Odorintensity in apparel fabrics and the link with bacterial populations. Textile ResearchJournal,77,449-56.

McQueen, R.H., Laing, R.M., Wilson, C.A., Niven, B.E., and Delahunty, C.M.,2007b.Odorretentiononapparelfabrics:Developmentoftestmethodsforsensorydetection.TextileResearchJournal,77,645-52.

Onions, W. J., 1962. Wool. An Introduction to its Properties, Varieties, Uses andProduction.IntersciencePublishers:46-63.

Pessenhofer,H.,B.Kohla,etal.,1991.Influencingenergyreadinessand thermal regulation of humans during physical stress on a bicycle ergometer by clothing made from various textile materials. Graz, Austria, Physiologiches Institut, Karl-Franzens Universitat.

Pierce,F.TandRees,W.H.1946.Heattransferthroughmoistfabrics.JournaloftheTextileInstitute,37,T181-204.

Reinert, G., Fuso, F., Hilfiker, R., and Schmidt, E., 1997. Textile Chemist and Colorist, 29: 12, 36.

Rodahl,R.,Giere,A.,Staft,P.H.,andWedin,B.,1973.Aphysiologicalcomparison of the protective value of nylon and wool in a cold environment, in A. Borg and J. H. Veghte (eds.), The Physiology of Cold Weather Survival (AGARDReportNo620)53-8.

Rodwell, E. C., Renbourn, E. T., Greenland, J., and Kenchington, K. W. L., 1965. An investigation of the physiological value of sorption heat in clothing assemblies.JournaloftheTextileInstitute,56,624-45.

VanderMerwe,J.P.andE.Gee,1985.TheEffectofFibrePhysicalProperties on Woollen Processing Performance and on Yarn and Plain Knitted Fabric Properties. Proceedings of the 7th International Wool Textile ResearchConference.Tokyo.2:95-104.

This report was prepared by the New Zealand Merino Company Limited, funded by WR Inc.