AbstractLow‐melting thermobonding PET (copolymer) fibers were used to produce heather effects in fabrics blended with cotton, which could be classified as natural 100% cotton fabrics. PET (copolymer) fibers produced at relatively low molecular weights with intrinsic viscosities of 0.57 and 0.47 were used in this investigation. These were mostly amorphous fibers that showed a low specific gravity at 1.27 g cm−3. The fibers were blended with cotton to produce open‐ended spun yarns without the PET component being melted. These yarns were knit into fabrics and cured. The curing was based on the thermal behavior of these fibers as observed in differential scanning calorimetry thermograms. The amount of pigmented PET copolymer needed to achieve the required heather effect was optimized by variations of the blend ratios. This approach provided another avenue for introducing additional functional properties, such as antibacterial and soil‐resistance properties, to the fabric. Both the fibers and resultant fabric properties were studied extensively, along with the finishing of these fabrics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3747–3756, 2003