This study focused on the production of heat storage materials from cotton wastes by incorporating a phase-change material and determination of their thermo-regulating properties. Polyethylene glycol (PEG) was grafted onto a cellulosic cotton backbone to give solid-solid phase change properties. The change in the surface morphology of the fibers was studied by scanning electron microscopy. Chemical characterization of the fibers was carried out using Fourier-transform infrared radiation spectroscopy. Thermal analysis of the modified fibers was performed by differential scanning calorimetry, and the thermal regulating properties of the PEG-grafted fibers were investigated using a thermal history system comprising insulated boxes, temperature sensors and a data-logger. Static thermal insulation measurements were also carried out on the fibers. The PEG-grafted cellulose fibers were shown to absorb up to 33.8J/g heat at 33.0?, releasing 31.5J/g heat at 29.4?, during the phase transitions. Thermal history results showed that temperature of the box containing PEG1000-incorporated fiber differed by 1-1.5 +/- 0.1? from the temperature of the box containing untreated cotton fibers over 23-25 minutes. Based on these results it is concluded that PEG-grafted cellulose has sufficiently high energy storage properties to be employed as a thermo-regulating material.