A method of selectively removing two or more isolation devices from a wellbore, which method comprises: introducing the two or more isolation devices into the wellbore, wherein the two or more isolation devices create at least two wellbore intervals (26, 27, 28, 29) by blocking or restricting fluid communication between the at least two wellbore intervals, and wherein each isolation device comprises a material, wherein each of the materials degrades within the wellbore, and wherein the degradation rate of each of the materials causes fluid communication to be restored between the wellbore intervals in a desired amount of time, and, wherein at least one of the isolation devices is a ball, and characterized in that: (i) the material of one or more of the isolation devices comprises a composition of two or more substances (51, 52); (ii) the isolation devices further comprise an insulator additive, said insulator additive physically separates the substances (51, 52), and (iii) at least two isolation devices comprise a different composition from each other, whereby the desired amount of time for restoring fluid communication for at least two of the wellbore intervals is different from each other; and causing or allowing each of the materials to degrade; allowing at least a portion of each of the two or more isolation devices to be removed from the bottomhole in a desired sequence; and restoring fluid communication between the at least two wellbore intervals in the desired amount of time. introducing the two or more isolation devices into the wellbore, wherein the two or more isolation devices create at least two wellbore intervals (26, 27, 28, 29) by blocking or restricting fluid communication between the at least two wellbore intervals, and wherein each isolation device comprises a material, wherein each of the materials degrades within the wellbore, and wherein the degradation rate of each of the materials causes fluid communication to be restored between the wellbore intervals in a desired amount of time, and, wherein at least one of the isolation devices is a ball, and characterized in that: (i) the material of one or more of the isolation devices comprises a composition of two or more substances (51, 52); (ii) the isolation devices further comprise an insulator additive, said insulator additive physically separates the substances (51, 52), and (iii) at least two isolation devices comprise a different composition from each other, whereby the desired amount of time for restoring fluid communication for at least two of the wellbore intervals is different from each other; and (i) the material of one or more of the isolation devices comprises a composition of two or more substances (51, 52); (ii) the isolation devices further comprise an insulator additive, said insulator additive physically separates the substances (51, 52), and (iii) at least two isolation devices comprise a different composition from each other, whereby the desired amount of time for restoring fluid communication for at least two of the wellbore intervals is different from each other; and causing or allowing each of the materials to degrade; allowing at least a portion of each of the two or more isolation devices to be removed from the bottomhole in a desired sequence; and restoring fluid communication between the at least two wellbore intervals in the desired amount of time.