The miscibility of the blown film of low- and high-density polyethylene blends and its implications on melting, crystallization, and mechanical behavior throughout the full composition range and the possible role of blending on the miscibility of the binary pair system have been investigated. Using differential scanning calorimetry it was inferred that the films of blends in solid state are miscible in HDPE-rich compositions, partially miscible at 95% LDPE and completely immiscible at other compositions. The thermal analysis revealed that blending has insignificant effect on lamella thickness of LDPE phase but strong influence on the lamella thickness of HDPE phase. Moreover, analysis of crystallization exotherms was also discussed. XRD measurements also revealed qualitatively similar trend in crystallinity and lamella thickness to DSC results. Measurements on tensile properties in the machine direction of the films showed both positive and negative deviation from linear additivity and improvement of the mechanical properties was found in the film blends containing low amount of LDPE. Especially the strain at break and tensile strength for the film of 5% LDPE blend was higher than that of neat HDPE, which suggests synergistic effects. This supports its larger lamella thickness and better miscibility. Nonetheless, there was negative deviation from the additivity rule in the entire range of composition for the mechanical properties in the transverse direction of the films. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012