The mass transfer coefficients for water vapor transfer through various clothing materials were obtained by measuring the water vapor transfer through the materials from air flow of high humidity into that of low humidity. The mass transfer coefficient of one sheet of cloth was determined by using the additive rule of mass transfer resistances from the overall mass transfer coefficients for one sheet and two sheets of cloth. The value of mass transfer coefficient for most of the cloth was around 10^-5mol/(m²s･Pa), but the value for the cloth woven with untwisted yarn of linear fiber was very small, at around 10^-7mol/(m²s･Pa). The tortuosity factor for water vapor diffusion in air pores within the cloth was calculated from the mass transfer coefficient by using the cloth thickness and fiber volume fraction, which increases with the increase in the fiber volume fraction. A correlation equation between the tortuosity factor and the fiber volume fraction within the cloth was obtained, which can be used to estimate the mass transfer coefficient of cloth from the cloth thickness and fiber volume fraction. The tortuosity factor depends on the shape of the fiber, the structure of the yarn and the woven structure of the cloth, and its value is large for the cloth woven with untwisted yarn of linear fiber. Hydrophilic -hydrophobic characteristics of fiber do not affect the tortuosity factor.