The isotherms for the sorption of water by six rubbery binders of the sort used in solid propellants have been measured at room temperature. The solubility at saturation ranged from 0.003 to 0.030 g. of water/g. of binder. The Flory-Huggins equation was used to calculate an upper limit for the x1 interaction parameters; these ranged from 2.6 to 4.7. The isotherms were best fitted by a modified Henry's law equation:
The possible significance of the parameters k, α, β, and Smax is discussed.