Mark Perry
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The structural parameter (S-value) of a forward osmosis membrane determines how severely the membrane is affected by concentration polarization

This makes the S-value one of the 3 most important FO membrane performance parameters besides the pure water membrane permeability coefficient (A) and the salt permeability coefficient (B).

ForwardOsmosisTech recently published an easy-to-use calculator for estimating FO membrane S-values. We hope you find it of use to your work.

As always, feel free to drop us a line at with any feedback or comments to our work.


  1. A question from Mohammed related to determining the S-value of forward osmosis membranes:

    Thank you so much for your website
    Well, I am a PhD student and my research is focusing in the usage of FO for oil industry.

    A quick question if you don’t mind please; Do you think S value should be used as a fixed and constant value even when the draw solution and flow rate (assume shell flowrate) are changing? I mean should we calculate S value for each draw solution at each respective flowrate??


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