Physical and chemical changes to the surface properties of wool fibre caused by exposure to RF generated plasma have been studied. Comparison is made between the changes for a wide range of plasma conditions and of the experimentally measured concentrations of the relevant neutral and charged particle species to elucidate those principally responsible and the likely mechanism. Results show that the measured increase in surface energy (from hydrophobic to hydrophilic) is well correlated with the integrated flux to the fibre of atomic oxygen, regardless of its origin. Charged particles appear to have little effect beyond sputtering, while the role of metastable excited oxygen molecules seems to be not statistically significant. Changes in surface chemistry shown by XPS are consistent with direct interaction of reactive � on the C-C and C-H bonds of the lipid layer which forms the outer (",,3 nm thick) layer of the natural fibre. Similar but weaker effects sometimes seen with discharges in argon appear to be due to the presence of oxygen as an impurity.