Roger L. Barker

From fabric hand to thermal comfort: the evolving role of objective measurements in explaining human comfort response to textiles

This paper traces the evolution of objective measurement of textile hand and comfort from Pierce through modern methodology and approaches. Special emphasis is given to discuss the contribution of the Kawabata Evaluation System (KES) towards advancing the state of objective measurement. Laboratory case studies are used to show how data generated by the KES and other instruments can be integrated into a comprehensive approach that attempts to explain human comfort response to garment wear in terms of fabric mechanical, surface and heat and moisture transfer properties.

Effects of Moisture on the Thermal Protective Performance of Firefighter Protective Clothing in Low-level Radiant Heat Exposures

This paper describes research on the effects of absorbed moisture on the thermal protective performance of the fire fighter turnout materials exposed to thermal assaults lower than flashover conditions. A thermal testing platform and sensor are used to measure thermal protective performance of turnout systems exposed to a sub flashover heat flux range 6.3 kw/m2 (0.15 cal/ cm2 s). The effects of moisture level on predicted second-degree burn injury for turnout systems having different moisture vapor permeability and total heat loss are discussed. Heat transfer analysis and experimental results show that, for selected test conditions, moisture negatively impacts protective performance most severely when the amount of added moisture is at a comparatively low level (15–20% of turnout system weight).

Modeling the Thermal Protective Performance of Heat Resistant Garments in Flash Fire Exposures

This research developes a numerical model to predict skin burn injury resulting from heat transfer through a protective garment worn by an instrumented manikin exposed to laboratory-controlled flash fire exposures. This model incorporates characteristics of the simulated flash fire generated in the chamber and the heat-induced changes in fabric thermophysical properties. The model also accounts for clothing air layers between the garment and the manikin. The model is validated using an instrumented manikin fire test system. Results from the numerical model help contribute to a better understanding of the heat transfer process in protective garments exposed to intense flash fires, and to establishing systematic methods for engineering materials and garments to produce optimum thermal protective performance.

In Vivo Cutaneous and Perceived Comfort Response to Fabric Part I: Thermophysiological Comfort Determinations for Three Experimental Knit Fabrics

Using a modified Kawabata Thermolabo apparatus housed in a controlled envi ronmental chamber, we obtained measurements of heat transfer through a specially selected set of jersey knit textile fabrics. We then used analytical models to compute thermal comfort limits based on the experimental values and predetermined estimates of human metabolic activity. The jersey knit fabrics differed primarily on the basis of fiber content: the comparisons were between two knits, both made with 100% polyester fibers of different deniers, and a 100% cotton fabric. This research confirms the results of several previous studies that fabric structural features, not component fibers, are the most important controllers of thermal dissipation in the presence of moisture diffusion. Our results also show that heat transfer is highly related to fabric thickness, bulk density, and air volume fraction. Thermal transfer from a simulated sweating skin surface is strongly correlated with fabric porosity and air permeability.

Effect of Moisture on the Thermal Protective Performance of Heat-Resistant Fabrics

The effect of fabric moisture on thermal insulation properties of twelve heat resistant fabrics made with polybenzimidazole (PBI), aromatic polyamide (aramid) and blends of PBI with aramid or with flame retardant rayon fibers is investigated in several high intensity radiant and convective heat exposures. Three fabric preparations were evaluated: oven dry samples, samples condi tioned in a standard atmosphere (65% R.H., 21 ° C) and samples soaked with liquid water. This research shows that moisture enhances the thermal in sulation of all single layer protective fabrics evaluated against 2.0 cal/cm2 ·sec mixed convective exposure and against 0.48 cal/cm2 · sec radiant energy expo sure. Moisture hurts the thermal protective performance (TPP) of the same fabrics in high intensity radiant tests (i.e., 2.0 cal/cm2 · sec, 100% radiant heat). The mechanisms by which moisture acts to change the TPP of a fabric is discussed in light of fabric heating rates.

Thermal Protective Performance of Heat-Resistant Fabrics in Various High Intensity Heat Exposures

The thermal protective performance of 21 heat-resistant fabrics made with poly benzimidazole (PBI), aromatic polyamide (aramid), and blends of PBI with aramid or with flame retardant rayon fibers was evaluated in laboratory tests using highly intense exposures to radiant or convective heat sources. The contribution of heat transfer mechanisms to thermal insulation is discussed, as is the degradation behavior of different materials in high intensity heating. Variables important in the development of improved fabrics for thermal protective apparel are identified.

Comfort Properties of Heat-Resistant Protective Workwear in Varying Conditions of Physical Activity and Environment. Part I: Thermophysical and Sensorial Properties of Fabrics

This series of studies investigates the impact of thermophysiologial and sensorial properties and end-use conditions of heat-resistant protective workwear on the wear comfort response. In Part I of this paper, material features and test methods are screened to obtain fabric characteristics that explain wear comfort effectively. Thermophysiological and sensorial properties including liquid moisture transfer properties are assessed for six heat resistant workwear materials with different fiber content, yarn property, weave type, and functional finishes. Based on the thermophysical values, small differences among the test garments are predicted. Measured sensorial properties, obtained from fabric mechanical, surface, and liquid moisture management properties, provide more distinctive comparisons. The remaining moisture (A) is calculated from the evaporated (E) and total driven (T) water to predict the sensation of clamminess after sweating. Results from surface roughness, contact area, and wet cling analysis show that softer yarns, finer fibers and twill weaves produce measurably smoother fabrics with small contact. Also, effects of hydrophilic fiber blending and wicking finishes on the moisture management properties are examined. The former does not affect the liquid moisture management properties while the latter measurably enhances the absorption rate. These results are discussed in relation to the wear comfort response in varying conditions of physical activity and ambient environments in Part II of this paper.

Handle of Weft Knit Fabrics

Two groups of weft-knitted fabrics, single and double knits, were selected to represent typical summer T-shirts and winter sportswear such as sweaters and other knit tops. Two kinds of analyses were performed: subjective overall handle and primary sensory factors were evaluated using a 99 point polar-word scale, and physical and thermal properties were characterized using the Kawabata evaluation system. Regression analysis was used to relate subjective and objective measurements. The handle of single knits was strongly related to the perception of softness and lightness; the handle of double knits was influenced by the perception of slickness and tightness. Surface friction and weight were associated with the hand ranking of single knits. Fabric surface roughness and bending hysteresis were physical properties that correlated with the hand ranking for double knits. The handle of plain knit loop structures was rated better than that of tuck-loop knits. For summer T-shirt material, single jersey was the preferred choice; for winter sportswear, interlock knits were preferred to other double knits.

Moisture Vapor Transport Behavior of Polyester Knit Fabrics

A test method that measures microclimate drying time is used to compare the ability of different knit materials to dissipate moisture vapor from a saturated clothing environment to the ambient atmosphere. The performance assessment provided by this novel method is compared with those from common test methods. The latter include measures of the moisture vapor transmission rate provided by the upright cup and the evaporative thermal resistance provided by the sweating guarded hot plate procedure. Upright cup and sweating hot plate measurements are shown to be predominately influenced by fabric thickness, but microclimate drying time, or the time-dependent dissipation of accumulated moisture vapor, assessed by the new method is most influenced by the pore characteristics of the fabric. Moisture vapor transmission through fabrics is assumed to be controlled mostly by fiber, yarn, and fabric variables that determine fabric thickness and porosity. Therefore, constructional variables that lead to thin knit structures, with unobstructed interyarn pores, are shown to be important considerations for designing fabrics with optimum moisture vapor dissipation properties.

Comfort Properties of Heat Resistant Protective Workwear in Varying Conditions of Physical Activity and Environment. Part II: Perceived Comfort Response to Garments and its Relationship to Fabric Properties

Controlled garment wear trials are used to evaluate comfort response to a well-characterized set of heat-resistant workwear materials. Multiple categories of perceived comfort reactions to garment wear in diverse conditions are explained in terms of measured fabric properties assessed in Part I. The important role of fabric surface character, especially surface roughness and predicted skin contact area, is revealed. Fabric sweat management, measurable using a modified demand wettability test, is also identified as a useful predictor of moisture-related skin contact sensations. Heat-resistant fabric designs incorporating structural features that minimize skin contact, while also providing liquid absorption capacity, are predicted to show enhanced comfort performance. Blending of hydrophilic fibers and wicking finishes, however, do not necessarily improve the comfort perceptions in the tested scenarios. Selected fabric thermophysiological and sensorial properties are closely correlated with subjective comfort responses and the relationships are dependent on the wear conditions. Surface geometric roughness (SMD), number of contact points (n k), and bending and shear rigidities are the decisive properties related to the tactile comfort. The vapor buffering index (B d) and liquid management properties, such as absorbent capacity (V), initial rate (Q 1), and wet cling index (i k) are the correlated indicators of nonabsorbency, clinginess, and sensation of clamminess. In particular, apparent water ratio (A/T), which can be assessed by a modified demand wettability test, is a good predictor of perception of clamminess in the cool-down period after exercise or a hot situation.