Hi, I received an excellent discussion on water vapor from Gordon Davy, I put a copy on my site for anyone who is interested. www.kondner.com/files/Vapor.pdf Seems to answers all my questions about Relative vs Absolute humidity and diffusion into plastics. Bob K. ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________