A fiber comprising (a) a low crystallinity polymer and (b) a high crystallinity polymer, wherein said fiber is capable of undergoing plastic deformation upon elongation and wherein said low crystallinity polymer comprises at least one ethylene/a-olefin interpolymer, wherein the ethylene/a-olefin interpolymer satisfies one or more of the following criteria: (a) has a M w /M n from about 1.7 to about 3.5, at least one melting point, T m, in °C (degrees Celsius), and a density, d, g/cm 3 (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; (b) has a M w /M n from about 1.7 to about 3.5, and is characterized by a heat of fusion, ΔH in J/g, and a delta quantity, ΔT, in °C (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: ΔT > -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; (c) has a molecular fraction which elutes between 40°C and 130°C when fractionated using TREF, characterized in that the fraction has a molar comonomer content of at least 5 percent higher than that of a comparable random ethylene interpolymer fraction eluting between the same temperatures, wherein said comparable random ethylene interpolymer has the same comonomer(s) and has a melt index, density, and molar comonomer content (based on the whole polymer) within 10 percent of that of the ethylene/α-olefin interpolymer; (d) an average block index greater than zero and up to 1.0 and a molecular weight distribution, M w /M n, greater than 1.3; and (e) at least one molecular fraction which elutes between 40°C and 130°C when fractionated using TREF, characterized in that the fraction has a block index of at least 0.5 and up to 1. (a) has a M w /M n from about 1.7 to about 3.5, at least one melting point, T m, in °C (degrees Celsius), and a density, d, g/cm 3 (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; (b) has a M w /M n from about 1.7 to about 3.5, and is characterized by a heat of fusion, ΔH in J/g, and a delta quantity, ΔT, in °C (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: ΔT > -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; (c) has a molecular fraction which elutes between 40°C and 130°C when fractionated using TREF, characterized in that the fraction has a molar comonomer content of at least 5 percent higher than that of a comparable random ethylene interpolymer fraction eluting between the same temperatures, wherein said comparable random ethylene interpolymer has the same comonomer(s) and has a melt index, density, and molar comonomer content (based on the whole polymer) within 10 percent of that of the ethylene/α-olefin interpolymer; (d) an average block index greater than zero and up to 1.0 and a molecular weight distribution, M w /M n, greater than 1.3; and (e) at least one molecular fraction which elutes between 40°C and 130°C when fractionated using TREF, characterized in that the fraction has a block index of at least 0.5 and up to 1.