Comparison of water vapor transmission rates using different measurement methods

Abstract

Water vapor transmission rates of films were measured by Japanese testing laboratories and the authors using six different methods. The results were analyzed through comparison. The measurement range was from 10⁻³ to 20 g m⁻² day⁻¹ at 40 °C and 90 % relative humidity. Two commercially available clay nanocomposite gas barrier films and three reference films with a small hole were used as samples. The measurements agreed within ±30 % in the range from 1 to 20 g m⁻² day⁻¹ and within ±50 % at around 0.1 g m⁻² day⁻¹. The agreement declined as the water vapor transmission rate decreased. The maximum differences were approximately 13-fold in the measurements of less than 0.1 g m⁻² day⁻¹. The origin of these differences was discussed.