A flexible non-crosslinked polyolefin thermal insulation foam and which is obtainable by extruding a mixture comprising: i) an ethylene/ α-olefin block copolymer, which comprises blocks of: A) crystalline or semi-crystalline blocks characterized by comprising ethylene in an amount of higher than 95 weight %; and B) elastomeric blocks characterized by comprising ethylene in an amount of 95 weight % or less and a comonomer content of 5 weight % or higher; and wherein the ethylene/ α-olefin block copolymer comprises alternating blocks of crystalline blocks of linear medium-density polyethylene, wherein medium-density is defined by a density range of 0,926-0,940 g/cm 3, and elastomeric blocks of ethylene/1-octene; ii) one or more random polymers with a density of between 0,880 g/cm 3 and 0,960 g/cm 3, selected from the group of a metallocene polyethylene and/or a polyethylene; and iii) a cell stabilizer; wherein the mixture comprises between 20 and 75 weight % of said ethylene/ α-olefin block copolymer under i); in a process comprising the steps of a) melting said mixture in the melting zone(s) of the extruder adjusted to temperatures of 160 to 220°C, at a pressure increasing from 1 bar up to 400 bar, b) injecting a physical blowing agent at an injection temperature of 140 to 220°C and an injection pressure of 30 to 300 bar, c) cooling the molten mixture in one or more cooling zones adjusted to temperatures of 85 to 115°C, and d) extruding the mixture through an extrusion nozzle adjusted to a temperature of 85 to 115°C and a pressure sufficiently high to keep any gas present in the mixture dissolved in the mixture; and wherein the thermal insulation foam has a percentage of open cells of 6 (+/-3) % or less based on the total cells in the foam. i) an ethylene/ α-olefin block copolymer, which comprises blocks of: A) crystalline or semi-crystalline blocks characterized by comprising ethylene in an amount of higher than 95 weight %; and B) elastomeric blocks characterized by comprising ethylene in an amount of 95 weight % or less and a comonomer content of 5 weight % or higher; and wherein the ethylene/ α-olefin block copolymer comprises alternating blocks of crystalline blocks of linear medium-density polyethylene, wherein medium-density is defined by a density range of 0,926-0,940 g/cm 3, and elastomeric blocks of ethylene/1-octene; A) crystalline or semi-crystalline blocks characterized by comprising ethylene in an amount of higher than 95 weight %; and B) elastomeric blocks characterized by comprising ethylene in an amount of 95 weight % or less and a comonomer content of 5 weight % or higher; and ii) one or more random polymers with a density of between 0,880 g/cm 3 and 0,960 g/cm 3, selected from the group of a metallocene polyethylene and/or a polyethylene; and iii) a cell stabilizer; a) melting said mixture in the melting zone(s) of the extruder adjusted to temperatures of 160 to 220°C, at a pressure increasing from 1 bar up to 400 bar, b) injecting a physical blowing agent at an injection temperature of 140 to 220°C and an injection pressure of 30 to 300 bar, c) cooling the molten mixture in one or more cooling zones adjusted to temperatures of 85 to 115°C, and d) extruding the mixture through an extrusion nozzle adjusted to a temperature of 85 to 115°C and a pressure sufficiently high to keep any gas present in the mixture dissolved in the mixture; and