A composition comprising: A) a thermoplastic polymer composition, and B) an impact modifying amount of an ethytene/α-olefin interpolymer, wherein the ethylene/α-olefin interpolymer is a block interpolymer comprising at least 50 mole percent methylene and: (a) has a Mw/Mn from 1.7 to 3.5, at least one melting point, Tm, in degrees Celsius, and a density, d, in grams/cubic centimeter, wherein the numerical values of Tm and d correspond to the relationship: T m > − 2002.9 + 4538.5 d − 2422.2 d 2; or (b) has a Mw/Mn from 1.7 to 3.5, and is characterized by a heat of fusion, ΔH in J/g, and a delta quantity, ΔT, in degrees Celsius defined as the temperature difference between the tallest DSC peak and the tallest CRYSTAF peak, wherein the numerical values of ΔT and ΔH have the following relationships: ΔΤ > − 0, 1299 ΔH + 62.81 for ΔH greater than zero and up to 130 J/g, ΔT ≥ 48 °C for ΔH greater than 130 J/g, wherein the CRYSTAF peak is determined using at least 5 percent of the cumulative polymer, and if less than 5 percent of the polymer has an identifiable CRYSTAF peak, then the CRYSTAF temperature is 30°C; or (c) is characterized by an elastic recovery, Re, in percent at 300 percent strain and 1 cycle measured with a compression-molded film of the ethylene/α-olefin interpolymer, and has a density, d, in grams/cubic centimeter, wherein the numerical values of Re and d satisfy the following relationship when ethytene/α-olefin interpolymer is substantially free of a cross-linked phase: Re > 1481 − 1629 d; or (d) has a comonomer content of a TREF fraction which elutes between 40°C and 130°C greater than or equal to the quantity (-0.2013)T + 21.07, where T is the numerical value of the peak ATREF elution temperature, measured in °C. A) a thermoplastic polymer composition, and B) an impact modifying amount of an ethytene/α-olefin interpolymer, wherein the ethylene/α-olefin interpolymer is a block interpolymer comprising at least 50 mole percent methylene and: (a) has a Mw/Mn from 1.7 to 3.5, at least one melting point, Tm, in degrees Celsius, and a density, d, in grams/cubic centimeter, wherein the numerical values of Tm and d correspond to the relationship: T m > − 2002.9 + 4538.5 d − 2422.2 d 2; or (b) has a Mw/Mn from 1.7 to 3.5, and is characterized by a heat of fusion, ΔH in J/g, and a delta quantity, ΔT, in degrees Celsius defined as the temperature difference between the tallest DSC peak and the tallest CRYSTAF peak, wherein the numerical values of ΔT and ΔH have the following relationships: ΔΤ > − 0, 1299 ΔH + 62.81 for ΔH greater than zero and up to 130 J/g, ΔT ≥ 48 °C for ΔH greater than 130 J/g, wherein the CRYSTAF peak is determined using at least 5 percent of the cumulative polymer, and if less than 5 percent of the polymer has an identifiable CRYSTAF peak, then the CRYSTAF temperature is 30°C; or (c) is characterized by an elastic recovery, Re, in percent at 300 percent strain and 1 cycle measured with a compression-molded film of the ethylene/α-olefin interpolymer, and has a density, d, in grams/cubic centimeter, wherein the numerical values of Re and d satisfy the following relationship when ethytene/α-olefin interpolymer is substantially free of a cross-linked phase: Re > 1481 − 1629 d; or (d) has a comonomer content of a TREF fraction which elutes between 40°C and 130°C greater than or equal to the quantity (-0.2013)T + 21.07, where T is the numerical value of the peak ATREF elution temperature, measured in °C. (a) has a Mw/Mn from 1.7 to 3.5, at least one melting point, Tm, in degrees Celsius, and a density, d, in grams/cubic centimeter, wherein the numerical values of Tm and d correspond to the relationship: T m > − 2002.9 + 4538.5 d − 2422.2 d 2; or (b) has a Mw/Mn from 1.7 to 3.5, and is characterized by a heat of fusion, ΔH in J/g, and a delta quantity, ΔT, in degrees Celsius defined as the temperature difference between the tallest DSC peak and the tallest CRYSTAF peak, wherein the numerical values of ΔT and ΔH have the following relationships: ΔΤ > − 0, 1299 ΔH + 62.81 for ΔH greater than zero and up to 130 J/g, ΔT ≥ 48 °C for ΔH greater than 130 J/g, wherein the CRYSTAF peak is determined using at least 5 percent of the cumulative polymer, and if less than 5 percent of the polymer has an identifiable CRYSTAF peak, then the CRYSTAF temperature is 30°C; or (c) is characterized by an elastic recovery, Re, in percent at 300 percent strain and 1 cycle measured with a compression-molded film of the ethylene/α-olefin interpolymer, and has a density, d, in grams/cubic centimeter, wherein the numerical values of Re and d satisfy the following relationship when ethytene/α-olefin interpolymer is substantially free of a cross-linked phase: Re > 1481 − 1629 d; or (d) has a comonomer content of a TREF fraction which elutes between 40°C and 130°C greater than or equal to the quantity (-0.2013)T + 21.07, where T is the numerical value of the peak ATREF elution temperature, measured in °C.