The determination of whether two dissimilar polymers are weldable is still largely trial-and-error. Here we suggest a correlation between laser weld strength and the ratio of the equilibrium interpenetration depth (w(infinity)) of two immiscible polymers to the maximum entanglement tube diameter of the two polymers (am). Taking the weld strength from a published chart of qualitative weld strength, we find a correlation coefficient between this and the ratio w(infinity)/a(max) of 0.67, where w. is based on the simple Hildebrand solubility parameter. This encouraged a quantitative study of the laser weld strength. This was done using a through transmission laser welding process with 0.4% carbon black as an absorber. The laser welds were tensile tested and relative weld strengths obtained. This strength was compared to the w(infinity)/a(max) ratio, where w. is based on experimentally determined Hansen solubility parameters. The results suggest weldability between dissimilar polymers is obtainable when w./amax is greater than 0.15. (C) 2013 Elsevier Ltd. All rights reserved.