The comfort of textiles is important and one area under evaluation is the development and application of Phase Change Materials, PCMs, in order to impart thermal adaptability. PCMs research for textiles has also focused on the use of polyethylene glycol (PEG). While there is a good adhesion between fibre and PEG polymer for cotton and polyester fibres, polymer adhesion to wool fibres appears poor and loosely bound within the yarn and had dislodged and crumbled. Therefore in this paper, the effect of changing the wool fibre surface energy and surface charge, shrinkproofing, on performance properties of thermally adaptable wool fabrics were studied. Untreated, gaseous fluorinated, as well as Chlorine-Hercosett treated 100 % wool fabrics have been evaluated to obtain highly cross-linked PEG with acceptable fastness properties. The surface interface was effectively probed by XPS & ToF-SIMS and characterised the loss of surface lipids, the nature of the fibre oxidation and deposition of Hercosett polymer on the wool fibre. The results indicate the necessity of having high surface energy in order to obtain appropriate adhesion and binding higher amount of solid polymer to wool fibres which results in superior thermal activity, better durability, and enhancement in felting performance.