1. It is shown that, in addition to the previously described steady decrease of tensile strength of vulcanizates during swelling, there are cases in which the strength passes through a maximum at low degrees of swelling. 2. Variations of a similar character during swelling are also found for the relative elongation of vulcanizates. 3. Such variations of tensile strength and relative elongation are found when the increase of chain flexibility and the associated increased orientation effect is greater than the effect of weakened intermolecular bonding in the polymer caused by penetration of the solvent molecules into the polymer. 4. A strength maximum may also be found if the swelling agent (softener) is introduced into the rubber composition on rolls before vulcanization.