We evaluated the inline birefringence of two blend systems in film blowing. The first system consisted of a metallocene catalyzed linear low density polyethylene (mLLDPE-1) and a low density polyethylene (LDPE-1); the second one was made of a metallocene catalyzed polyethylene containing sparse long chain branches (mLLDPE-2) and another low density polyethylene (LDPE-2). Experimental data show that before the crystallization starts, the birefringence of the mLLDPE-2/ LDPE-2 blends is a linear function of blend composition, suggesting miscibility of the mLLDPE-2/LDPE-2 blends. However, the birefringence of the mLLDPE-1/LDPE-1 blends shows positive deviations with respect to a linear function of blend composition. This is caused by the existence of form birefringence, suggesting immiscibility of the mLLDPE-1/LDPE-1 blends. The nonuniform biaxial elongational viscosity (NUBEV) at the reference temperature of 175 degrees C for LDPE-1 was evaluated for different operating conditions. The results show that NUBEV is approximately a unique function of the deformation rate, confirming the validity of the assumptions and technique used for the NUBEV calculation. The NUBEV and the nonuniform biaxial Trouton ratio (NUTR) of the mLLDPE-2/LDPE-2 blends was also evaluated using the same technique. The NUBEV of all mLLDPE-2/ LDPE-2 blends shows a strain-thinning behavior within the deformation rates investigated. Furthermore, the NUTR results show that LDPE-2 deviates largely from the Newtonian fluid behavior, whereas mLLDPE-2 is quite close to the Newtonian behavior. Nevertheless, the NUTR of the mLLDPE-2/LDPE-2 blends is almost a linear function of blend composition. (c) 2005 Society of Plastics Engineers.