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 by blocking or restricting fluid communication between the at least two wellbore intervals (26-29), 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 ; (ii) the isolation devices further comprise an insulator additive , said insulator additive physically separates the substances , 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 (26-29) 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 by blocking or restricting fluid communication between the at least two wellbore intervals (26-29), 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 ; (ii) the isolation devices further comprise an insulator additive , said insulator additive physically separates the substances , 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 ; (ii) the isolation devices further comprise an insulator additive , said insulator additive physically separates the substances , 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 (26-29) in the desired amount of time. <EOS>