A terpolymer composition comprising: A) From 80 wt% to 97 wt% of a propylene, ethylene, 1-butene terpolymer having: i) the content of ethylene derived units ranging from 0.5 wt% to 3.2 wt%, measured according to the method defined in the description; ii) the content of 1-butene derived units ranging from 7.2 wt% to 14.8 wt%, measured according to the method defined in the description; iii) the xylene soluble fraction at 25°C ranging from 7.2 wt% to 13.4 wt%, measured according to the method defined in the description; iv) the melting point determined by differential scanning calorimetry, according to ISO 11357-3, with a heating rate of 20 °C/minute ranging from 123°C to 138 °C; v) the C 13 NMR sequences EEE ranging from 0.16 mol% to 0.40 mol%, measured according to the method defined in the description; vi) the melt flow rate, MFR, measured according to ISO 1133 at 230 °C with a load of 2.16 kg, ranging from 1.0 g/10 min to 20.0 g/10 min; B) From 20 wt% to 3 wt%; of a propylene, ethylene, 1-butene terpolymer having: i) the content of ethylene derived units ranging from 0.5 wt% to 3.2 wt%; ii) the content of 1-butene derived units ranging from 14.4 wt% to 26.5 wt%; iii) the xylene soluble fraction at 25°C ranging from 38.2 wt% to 60.2 wt%; wherein the content of 1-butene derived units of component A) is lower than the amount of the content of 1-butene derived units of component B); and the terpolymer composition having the melt flow rate, MFR, measured according to ISO 1133 at 230 °C with a load of 2.16 kg, ranging from 3.0 g/10 min to 20.0 g/10 min; the sum of the amounts of A) and B) being 100 wt%. A) From 80 wt% to 97 wt% of a propylene, ethylene, 1-butene terpolymer having: i) the content of ethylene derived units ranging from 0.5 wt% to 3.2 wt%, measured according to the method defined in the description; ii) the content of 1-butene derived units ranging from 7.2 wt% to 14.8 wt%, measured according to the method defined in the description; iii) the xylene soluble fraction at 25°C ranging from 7.2 wt% to 13.4 wt%, measured according to the method defined in the description; iv) the melting point determined by differential scanning calorimetry, according to ISO 11357-3, with a heating rate of 20 °C/minute ranging from 123°C to 138 °C; v) the C 13 NMR sequences EEE ranging from 0.16 mol% to 0.40 mol%, measured according to the method defined in the description; vi) the melt flow rate, MFR, measured according to ISO 1133 at 230 °C with a load of 2.16 kg, ranging from 1.0 g/10 min to 20.0 g/10 min; i) the content of ethylene derived units ranging from 0.5 wt% to 3.2 wt%, measured according to the method defined in the description; ii) the content of 1-butene derived units ranging from 7.2 wt% to 14.8 wt%, measured according to the method defined in the description; iii) the xylene soluble fraction at 25°C ranging from 7.2 wt% to 13.4 wt%, measured according to the method defined in the description; iv) the melting point determined by differential scanning calorimetry, according to ISO 11357-3, with a heating rate of 20 °C/minute ranging from 123°C to 138 °C; v) the C 13 NMR sequences EEE ranging from 0.16 mol% to 0.40 mol%, measured according to the method defined in the description; vi) the melt flow rate, MFR, measured according to ISO 1133 at 230 °C with a load of 2.16 kg, ranging from 1.0 g/10 min to 20.0 g/10 min; B) From 20 wt% to 3 wt%; of a propylene, ethylene, 1-butene terpolymer having: i) the content of ethylene derived units ranging from 0.5 wt% to 3.2 wt%; ii) the content of 1-butene derived units ranging from 14.4 wt% to 26.5 wt%; iii) the xylene soluble fraction at 25°C ranging from 38.2 wt% to 60.2 wt%; wherein the content of 1-butene derived units of component A) is lower than the amount of the content of 1-butene derived units of component B); and i) the content of ethylene derived units ranging from 0.5 wt% to 3.2 wt%; ii) the content of 1-butene derived units ranging from 14.4 wt% to 26.5 wt%; iii) the xylene soluble fraction at 25°C ranging from 38.2 wt% to 60.2 wt%; wherein the content of 1-butene derived units of component A) is lower than the amount of the content of 1-butene derived units of component B); and the terpolymer composition having the melt flow rate, MFR, measured according to ISO 1133 at 230 °C with a load of 2.16 kg, ranging from 3.0 g/10 min to 20.0 g/10 min; the sum of the amounts of A) and B) being 100 wt%.