The concept of double networks is a rather new idea, by which one imparts chain orientation in elastomers. Double networks were made in natural rubber vulcanizates cured with a single and a new binary accelerator system. Double networks with different extensions were prepared and their effects on tensile properties were analyzed. The influence of extent of initial cure on double-network formation was examined. Thermal stability of the double network formed was analyzed by ageing of the double networks and was found to improve with residual extension. Crosslink density of the networks formed was determined by swelling methods and stress-strain analysis. it was found that crosslink density increased with double-network formation and residual extension. The stress-strain behavior and moduli were analyzed to study the effect of these properties on double-network formation. Double networks were hardly affected by the binary accelerator system. Based on the studies it was found that residual extension was the major factor determining the final properties. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1068-1076, 2004.