Air Permeability and Water Vapour Transmission in Hemp-Blended Denim Fabrics: A Comparative Study of Hemp Blend Ratio, Weft Count and Dual-Core Weft Architecture

This study comparatively examines the combined influence of hemp blend ratio, weft count and dual-core weft architecture on selected transport-related comfort indicators of hemp-blended denim fabrics. Eleven 3/1 twill denim fabrics were produced using two warp families, namely 100% cotton and cotton/hemp (69/31), together with rigid, single-core and dual-core weft yarns incorporating cotton, hemp, lyocell, elastane and PET/PTT T400®. Air permeability was measured according to ASTM D737, and the water vapour transmission factor (WVPf) was determined using a wet-cup gravimetric procedure based on ASTM E96. Air permeability ranged from 96.68 to 252.96 mm/s, while mean WVPf values ranged from 102.89 to 204.28. The results indicated that weft architecture and fabric structure were more strongly associated with comfort behaviour than fibre composition alone. In particular, dual-core weft constructions generally promoted higher air permeability, whereas water vapour transmission remained dependent on a combined effect of fabric mass, sett and yarn design. Fabrics containing hemp contributed to moisture transfer performance, although the magnitude of this effect varied with constructional parameters. Multivariate evaluation further indicated that fabric mass, ends/cm and picks/cm were key variables governing the observed comfort response. Overall, the findings suggest that hemp-blended denim fabrics can be optimised through an appropriate balance of hemp content, weft count and dual-core yarn design to achieve improved breathability and moisture transport.