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.