The permeation tubes were fabricated using polydimethylsiloxane (PDMS) and their permeation behaviour of water vapour was investigated under different experimental conditions. Experimental results showed that the permeation rate through PDMS wall was largely dependent on tube material and temperature. Permeation rate of water through PDMS shows approximately 100 times higher than that of tetrafluoroethylene-hexafluoropropylene copolymer. High concentration of standard water vapour can be made due to their superior permeation rate. It was also observed that the phase of water (liquid or vapour) and its distribution in the tube significantly affected permeation rate of water and it behaves as a main uncertainty factor on the consistency of permeation rate. Liquid water showed approximately twice higher permeation rate than vapour did. Moreover, an uneven distribution of water in the permeation tube affected the consistency of permeation rate with respect to time. The results illustrated the rationale of gradual decrease in the permeation rate of water through the permeation tubes. Based on the results, a novel experimental setup of permeation tube was proposed to maximise the consistency of water permeation rate. The change in permeation rates of newly designed tubes was less than 2% until water in the tube was exhausted. (C) 2009 Elsevier B.V. All rights reserved.