Relationship between wearer prickle response with fibre and garment properties and Wool ComfortMeter assessment

The prickle evoked by 48 knitted fabrics was assessed by wearers under a defined evaluation protocol. The relationship between the average wearer prickle score and known properties of constituent fibre, yarns and fabrics and fabric evaluation using the Wool ComfortMeter (WCM) was determined using linear modelling. After log transformation, the best model accounted for 87.7% of the variance. The major share of variation could be attributed to differences between mean fibre diameter (MFD) and WCM values. Low prickle scores were linearly associated with lower MFD, lower WCM and lower yarn linear density. There was an indication that yarn twist affected prickle scores and that fabrics composed of cotton evoked less prickle. Measures of fibre diameter distribution or coarse fibre incidence and other fabric properties were not significant. The analysis indicates that wool garments can be constructed to keep wearer assessed prickle to barely detectable levels and textile designers can manipulate a range of parameters to achieve similar wearer comfort responses.

Predicting comfort properties of knitted fabrics by assessing yarns with the Wool ComfortMeter

This study examined the feasibility of assessing yarns with the Wool ComfortMeter (WCM) to predict the comfort properties of the corresponding single jersey-knitted fabrics. The optimum yarn arrangement to predict the comfort value of a corresponding control fabric was determined using nine wool and wool/nylon-blended yarns (mean fibre diameter range 16.5–24.9 μm) knitted into 34 different fabrics. Using a notched template, yarn winding frequencies of 1, 3, 6, 12, 25 and 50 parallel yarns were tested on the WCM. The best predictor of fabric WCM values was using 25 parallel yarns. Inclusion of knitting gauge and cover factor slightly improved predictions. This indicates that evaluation at the yarn stage would be a reliable predictor of knitted fabric comfort, and thus yarn testing would avoid the time and expense of fabric construction.

The Wool ComfortMeter and the Wool HandleMeter, new opportunities for wool

Two instruments have been developed by the Sheep CRC that provide the tools for a new standard in comfort and handle for the next generation of next-to-skin wool knitwear. The Wool ComfortMeter and Wool HandleMeter provide a rapid, accurate and objective measure of two important characteristics of wool knitwear that are currently determined by subjective assessment. The Wool HandleMeter allows the prediction of a set of handle attribute values that can quantify the hand feel of a lightweight jersey fabric. The instrument uses the principle of pushing a fabric sample through a ring. The force displacement curve associated with the fabric test is characterised and used to define each fabric. These values were then compared to the average handle values, as determined by a group of experts, of a large set of lightweight knitted fabrics. Algorithms were developed that enable the instrument to more accurately predict each of seven handle attributes than an individual expert. The Wool ComfortMeter provides a measure of the fibres that are protruding from the surface of the fabric that are responsible for the itchy sensation caused by some knitwear. The results from the instrument have been compared to the results from extensive wearer trials to provide an understanding of the relationship between the instrument value and the comfort perceptions of wearers. The results have shown a very clear relationship between the instrument and wearer trials.

Associations between the physiological basis of fabric-evoked prickle, fiber and yarn characteristics and the Wool ComfortMeter value

The association between the incidents counted by the measurement wire of the Wool ComfortMeter (WCM) and the previously published neurophysiological basis for fabric-evoked prickle have been investigated for lightweight knitted woolen fabrics. The fiber lengths and diameters capable of triggering the fabric-evoked prickle sensation were calculated using Euler’s buckling formula, and it is suggested that fibers as fine as 10 mm are capable of triggering the prickle response if they have a short enough free length protruding from the surface. Good agreement was found between the sensory assessed human prickle sensation and the wearer prickle response predicted using the WCM outputs, especially when the latter were transformed using Stevens’s Psychophysical Power Law.

Predicting fabric prickle propensity by testing yarns on the Wool ComfortMeter

The Wool ComfortMeter is the first simple and fast objective tool in the world for assessing wool fabric prickle propensity. IWTO-DTM-66 for the measurement of fabrics using the WCM was accepted at the IWTO Cape Town Congress, South Africa in 2014. Since then, interest has been shown in the technology by yarn manufacturers and buyers for testing yarns before fabric is made, in order to obtain the prickle propensity of a fabric while still at yarn stage.Presentation of the yarn sample to the Wool ComfortMeter is critical. An YG381 yarn winder was selected for this project because it is a fast and reliable tool for sample preparation. The investigation into yarn winding density and tension showed that both the winding density and tension did not significantly affect the tested yarn WCM values. Therefore, a sample preparation protocol was established by using a winding density 19 loops/cm and a 20g tension plate on the YG381 winding machine.Further examination by complying with the preparation protocol showed that yarn Wool ComfortMeter value was the only significant predictor of its corresponding fabric Wool ComfortMeter value. Thus, liner and polynomial regression models were developed for predicting the fabric WCM prickle propensity. Based on the prediction performance, a linear model was recommended for the 1-ply yarns and polynomial model for the 2-ply yarns in this report. The prediction errors were approximately 66 for the 1-ply yarns and 14 for the 2-ply yarns.

Report on the second Wool ComfortMeter round trial

The present report analysed the variance between instruments and estimated the measurement precision of the Wool ComfortMeter instrument by conducting an international round trial. The firstinternational round trial was conducted in 2014; however the calculated precision estimates were relatively large. In the present trial, instruments were standardised by harmonising parameters such as wire height and measuring length, and a new calibration method was used to improve the measurement precision. The data from five laboratories, measuring ten fabric-samples and 5 sub-samples per fabric sample, was used to estimate the components of variance and the prickle measurement precision. The results showed good agreement between laboratory measurements. Analysis of the data shows an improvement in the 95% confidence limit for this round trial compared to the first round trial. Particularly, relatively smaller confidence limits were found for low prickle measurements. It is recommended that the new precision estimates be incorporated into the IWTO DTM-66:2014.

The effect of humidity and temperature on Wool Comfort Meter assessment of single jersey wool fabrics

The Wool ComfortMeter provides an objective measurement of the fabric-evoked prickle discomfort rating provided by wearers. This work aimed to quantify the sensitivity of the Wool ComfortMeter over a range of different temperature and humidity conditions to determine the recommended test conditions for its operation. The design was: three temperatures (notionally 20, 25 and 30°C) at three relative humidities (RHs, notionally 50, 65 and 80%) each with two replicates, using six different wool single jersey knits (mean fibre diameter 19.5–27.0 µm). As it was difficult to achieve exactly some of the extreme combinations of temperature and RH, some combinations were repeated, providing a total of 23 different assessment conditions. Data were analysed using restricted maximum likelihood mixed model analysis. The best fixed model included RH, RH2, temperature and the interaction of temperature and RH, accounting for 95% of the variation in Wool ComfortMeter readings. Wool ComfortMeter values were almost constant at 55–60% RH. Generally, the Wool ComfortMeter value reduced with increasing RH > 60% at temperatures of 25°C and 28.5°C as the regain of the fabric increased. However, at 20°C little change was detected as RH was increased from 50 to 80% as there were only small changes in fabric regain. The observed effects were in a good agreement with existing knowledge on the effect of regain on the mechanical properties of wool fibre. Wool ComfortMeter is best operated under standard conditions for textile testing of 65% RH and 20°C.

Effect of fibre, yarn and knitted fabric attributes associated with wool comfort properties

In this replicated experiment, we investigated the comfort properties of single jersey fabrics composed of cashmere in blends with superfine wools of different fibre curvature (crimp) where the fibre diameter of the wool and cashmere were tightly controlled. The 81 fabrics were evaluated using the Wool ComfortMeter (WCM) which has been calibrated using wearer trials of wool knitwear. General linear modelling determined the best prediction models for log10 transformed fabric WCM values using 27 fibre, 16 yarn and 30 fabric attributes. Tighter fabrics were less comfortable. Progressively blending cashmere with wool progressively increased comfort assessment. The WCM was able to detect differences between fabrics which were more supple and springy, thinner and lighter, and were composed of more elastic, uniform and stronger yarns. Together these attributes explained 82% of the variance in WCM value.

Effect of surface treatment and knit structure on comfort properties of wool fabrics

The comfort properties of the pique and single jersey knitted wool fabrics were investigated using the Wool ComfortMeter (WCM). The fabrics were knitted in three cover factors and treated with either plasma or a silicone softening agent and were compared with untreated fabrics. Plasma treatment did not show significant effects on the comfort value. However, silicone polymer significantly reduced WCM values suggesting that the silicone coating reduced the number of protruding fibres on the fabric surface. Regardless of treatment used, pique fabrics showed a lower WCM value, and therefore were perceived to be more comfortable than the single jersey structure. While the effect of cover factor was not significant, in fitted model to predict the WCM value of fabrics, mass/unit area and fabric thickness were significant predictors along with fabric structure and finishing treatment.

Relationships between wearer assessment and the instrumental measurement of the handle and prickle of knitted wool fabrics

The relationships between wearer-assessed comfort and objectively measured comfort and handle parameters were investigated using 19 pure wool single jersey garments made of single ply yarns. Wearer trials were used to determine prickle discomfort, and whether wearers “liked” the garments. Fabrics then were objectively evaluated using the Wool HandleMeter, which measures seven primary handle attributes; and the Wool ComfortMeter (WCM), to predict a wearer's perception of fabric-evoked prickle. Wearer responses and the relationships within and between objective measurements and the effect of fibre, yarn and fabrics attributes were analysed by general linear modelling. Mean fibre diameter, fibre diameter coefficient of variation, yarn count, fabric thickness, fabric density, fabric mass per unit area and decatising affected one or more handle parameters. The best model for predicting wearer prickle discomfort accounted for 90.9% of the variance and included only terms for the WCM and WCM2. The WCM was a good predictor whereas mean fibre diameter was a poor predictor of whether wearers “liked” garments. Wearer assessment of prickle and whether or not wearers “liked” fabrics were independent of fabric handle assessment. The results indicate that the handle and comfort properties of lightweight, wool jersey fabrics can be quantified accurately using the Wool HandleMeter and the Wool ComfortMeter. For fabric handle, fibre and yarn characteristics were less important than changes in the properties of the fabric.

Effects of variation in wool fiber curvature and yarn hairiness on sensorial assessment of knitted fabrics

Previous investigations have shown that prickle discomfort sensations of wool fabrics are primarily determined by the mean fiber diameter of the wool. It is also known that differences in wool fiber curvature (crimp) affect softness of handle of greasy wool and of wool textiles. In a replicated experiment, we investigated if wearers could detect the effect of using 17 µm superfine wool of low (74°/mm) or high (114°/mm) fiber curvature, and when the wools were blended with 17 µm cashmere (fiber curvature 49°/mm) in differing proportions, on four comfort sensations. Eight single jersey knitted fabrics were assessed under a controlled protocol using forearm sleeves made of the test fabric and a control fabric. Data (37 sensorial assessments of high curvature wool fabrics; 38 sensorial assessments of low curvature wool fabrics) were analyzed using linear mixed model analysis (restricted maximum likelihood), which included fixed effects for wool type and blend ratio and a random effect for participant. The use of a control sleeve fabric reduced variance due to participant effects by providing an anchor for each sensation over time. Wool fiber curvature affected participant assessment of breathability, comfort, feel after exercise (damp/dry) and skin feel (prickly/soft), with preferred values associated with high curvature (crimp) superfine wool. Increasing the proportion of cashmere in fabrics increased skin feel (better assessed softness). Skin feel was strongly associated with the evaluation of the fabrics by the Wool ComfortMeter and with increasing hairiness of yarns.

Relationships between sleeve trial and wearer trial assessment of discomfort and objective measurements

The relationships were investigated between the prickle discomfort scores, assessed by human response from wearer trial garment assessment, and sleeve trial, Wool ComfortMeter (WCM) and Wool HandleMeter (WHM) assessments of fabrics, and fiber diameter characteristics including mean fiber diameter (MFD). Sleeve trial assessment followed exercise, the use of a control sleeve to reduce participant variance and four sensory traits. WHM provides eight handle parameters calibrated against a panel of experts. Four scenarios were evaluated: sleeve trial assessment with MFD; sleeve trial assessment with MFD and WCM; sleeve trial assessment with MFD, WCM and WHM parameters; and sleeve trial assessment with WCM and WHM parameters. Data were analyzed using correlation and forward stepwise general linear modeling. There was no evidence that the incidence of fibers coarser than 30 µm aided the prediction of prickle discomfort once MFD had been accounted for in the models. There were significant correlations between the WCM measurement and each sleeve trial attribute. There was no significant correlation between WHM parameters and sleeve trial assessments. The sleeve trial attribute of ‘skin feel’ offers potential to improve the predictions made of wearer trial prickle discomfort when used in association of the WCM with or without data on fabric MFD. There was little evidence to support using WHM parameters with or without the WCM in predicting wearer assessed prickle discomfort of fabrics. These results indicate that the rapid evaluation of fabrics using sleeve trial assessment can provide cost effective ranking of consumer preferences.