An isolation device with seal element having substantial elongation properties at a time of setting and insubstantial elongation properties at time of drill out. That is, the seal element may be constructed of materials that are geared toward providing effective temporary sealing, for example to support stimulation operations. The seal is also tailored to change elongation properties over time such that upon sufficient exposure to downhole conditions the elongation properties may be substantially reduced. Thus, drillable removal of the device and seal element may be readily attained without undue concern over stretchable tearing of the element leading to an accumulation of large debris left behind in the well.