The main aspect of blending of two or more fibers in yarn manufacturing is production a yarn or fabric with superior properties. Fiber blending can enhance the quality of product that cannot be achieved using one fiber type alone, and it can also reduce the cost by substituting a less expensive fiber for a more costly one. Prediction of the blend properties or mixed materials is not limited just to the textile field. In general, if a material is a mixture of more than one constituent component, the overall properties of the blended system are obviously related to the relative proportion and corresponding properties of each component. The interactions of the components themselves complicate the relationship between the blended system and its component properties and cause that it does not follow from simple rule of mixture (ROM). In this study, 5 types of cotton/polyester blended yarns have been produced: 75/25, 62.5/37.5, 50/50, 37.5/62.5, 25/75 and 100% cotton, 100% polyester yarn. Various properties of yarns are examined and analyzed by statistical model. Then the results are compared with the Hamburger model for blended yarns and finally, the migration factor of yarn is assessed to trace the migration effect on the yarn properties. The effect of interaction is investigated on breaking load, breaking length, tenacity, strain, work of rupture, elastic modulus, thick place, thin place, nep, hairiness and uniformity properties in each yarn. The results of experiments have been compared with the predictions of ROM model by drawing the regression line from data. The difference between the regression line and simple models reveals the hybrid effect. The results show that the difference between two lines is not significant in breaking length, strain and thin place, but it is significant in other parameters. In comparison of hybrid and Hamburger model, it is demonstrated that the results do not follow Hamburger model due to difference in the structural properties of ring and rotor yarns. To achieve the highest tenacity, the best type of blended yarn is 75/25 PET/Co according to this work. The migration is one of the factors that influence the physical properties in yarns, so, the migration index has been calculated in blended yarns by taking 30 cross-sections in each blended yarn. This factor represents the actual migration of the component at yarn cross-section. It could been changed from -100 to +100 that represents the complete separation of the component from the other fibers in moving inward or outward, respectively. The results show that cotton fibers have migrated inward of cross-section in all of the yarns due to the cross-sectional shape and fineness. This factor is minimum at 75/25 PET/Co and maximum at 50/50 PET/Co blended yarns.