This thesis is concerned with the Transplanar wicking of water through multi-layer fabric assemblies, with particular reference to firefighters’ under garments. The literature survey is concerned with a review of research work carried out on thermophysiological comfort and the heat and moisture transmission in relation to clothing. This serves as an introduction to which the experimental work has been concerned with the design and construction of apparatus for the measurement of horizontal transplanar wicking (i.e. from a lower fabric layer to the adjacent upper fabric layers, laid horizontally). This apparatus has been constructed to allow the measurement of horizontal transplanar wicking under static fabric conditions, and another novel design has been built for horizontal transplanar wicking measurements under dynamic conditions. In addition a novel design of apparatus for the measurement of vertical transplanar wicking under static conditions has been designed and constructed. A series of horizontal transplanar wicking tests have been carried out on a range of lxl rib polypropylene, Nomex, and Coolmax (polyester) knitted fabrics, and cotton and acrylic interlock knitted fabrics. The initial wicking of water into the fabric occurs in the fine inter-fibre capillaries within the yam structure and then transplanar wicking occurs through contiguous inter-fabric contact points. The nature and number of these inter-fabric contact points in any two or more fabric layers has been demonstrated to depend upon the relative orientation of the fabric construction and the applied pressure. For these reasons some variability in the initial wicking stages of weft knitted fabrics is to be expected, as every two fabric layers in contact will exhibit different inter-fabric contact points. A model of horizontal transplanar wicking has been proposed to explain the observed phenomena. The type of water used (distilled) has been studied in comparison with deaerated and carbonated water, and been shown to have only a very minor influence on the initial rate of wetting and wicking. An empirical hyperbolic equation has been proposed to explain the results of the horizontal transplanar wicking in a single fabric layer which relates the change in percentage fabric water content (%) in a single layer to the wicking time. In this way any fabric under study may be characterised by the initial rate of wicking and the theoretical maximum fabric saturation can be calculated. The effect of modifying the fabric surface structure by singeing, rubbing, and brushing has been compared with the untreated state for cotton interlock fabric. Disruption of the fine capillaries within the yarn appears to have an adverse affect on the rate of wicking, also the type of disruption. The maximum fabric saturation also appears to be affected by the type of surface disruption which may occur in everyday clothing wear. Dynamic horizontal transplanar wicking exhibits greater transplanar wicking rates compared with the results on the same fabrics under static conditions. The results in each case are dependent upon which fabric type acts as the initial reservoir for transplanar wicking. It was observed that for cotton fabrics that wet out rapidly in vertical transplanar wicking, the initial fabric layer always maintains a greater amount of water than the fabric layer below, whereas the reverse occurred in fabric that were slow to wet out.