Abstract Binary surfactant mixtures have been much studied over the years for both great practical and theoretical importance. However, the mechanisms different nonionic surfactant types follow during aggregation into mixed micelles, and probably while forming a mixed surfactant adsorption layer are very poorly understood. Furthermore, the explanation for non-ideal behaviour of trisiloxane surfactant mixtures is still lacking. We have investigated binary mixtures of two commercial superspreaders, Silwet L-77® and Additive 67®, with conventional Triton X-100® surfactant. Observed non-ideal behaviour has been proven to be largely dependent on both total concentration of the binary surfactant mixture and the hydrophobicity of the substrate which it is spreading on. In addition to that, synergistic and antagonistic effects have been revealed and explanations for the observed strange behaviour suggested, with steric problems due to differences in geometry of the surfactant molecules being the key factor. We also showed that present impurities in commercial surfactants can play a major role in the performance of binary surfactant mixtures and that for certain applications mixtures of trisiloxanes with conventional surfactant can be more efficient than trisiloxanes alone.