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Introduction
Ventilation features are often cited as a possible solution to the problem of changing activity intensity (and thus metabolic heat output) requiring changes in clothing thermal insulation to maintain thermal balance: patents attempting to exploit ventilation date back more than a century ([6] Brinkmann, 1885; [24] Wellman, 1904). [1] Belding et al. (1947) observed that due to body movement induced air flow in and between the clothing layers, clothing thermal insulation was reduced by up to 44 per cent of its static value when running at six miles per hour, and suggested it may be possible to develop clothing which would provide appropriate insulation for any activity level by manipulating this effect. [10] Fourt and Hollies (1970) also identified ventilation as one of the most promising means of improving clothing for cold climates. More recently, [17] Lomax (2007) suggested that features which provide ventilation are of equal if not more importance than waterproof breathable fabrics, and other authors have suggested the necessity for more systematic research aiming to optimise ventilation features ([11] Ghaddar and Ghali, 2009).
Despite this, in a recent and comprehensive review, [16] Laing and Sleivert (2009) suggest that the effectiveness of vents in minimising adverse thermal effects is questionable. For example, observed differences in physiological parameters were small in studies with human subjects ([5] Breckenridge, 1977; [20] Ruckman et al. , 1998). In the first of these studies subjects performed exercise on cycle ergometers, where the upper body is relatively still and the arms fixed in position, with no simulated wind at a rather warm temperature of 20°C. These factors may explain why only small reductions in skin temperature were observed. In the earlier study vented back designs were only advantageous with impermeable materials; [16] Laing and Sleivert (2009) suggest that the relatively undemanding exercise regime may account for the lack any large observed differences. More promising results have been published by [23] Umbach (1981) who developed a clothing system with a carefully considered fabric structure and ventilated garment design which reportedly was comfortable to wear between -20°C and 16°C.
Tracer gas techniques have also been employed to elucidate the effect of clothing design on ventilation; [8] Crockford et al. (1972) pioneered this technique for clothing applications and later [2]...