A discontinuous process for producing a series of at least two articles containing thermally insulating polyurethane foam from at least (A) a first stream comprising at least one isocyanate reactive compound, (B) a second stream comprising at least one organic polyisocyanate, and (C) a third stream comprising at least one compound selected from isocyanate reactive compounds, organic polyisocyanates, catalysts, blowing agents, chain extenders, stabilizers, crosslinkers, flame retardants, and additives, wherein stream (C) is different from both streams (A) and (B); wherein the process comprises the steps (a) producing at least one first article by (a1) providing a first polyurethane reaction mixture in a mixing device (MD) by mixing at least streams (A), (B) and (C); (a2) injecting the first polyurethane reaction mixture provided in step (a1) into a cavity of the at least one first article and forming the thermally insulating polyurethane foam; and (b) producing at least one second article by (b1) providing a second polyurethane reaction mixture in the mixing device (MD) by mixing at least streams (A), (B) and (C); (b2) injecting the second polyurethane reaction mixture provided in step (b1) into a cavity of the at least one second article and forming the thermally insulating polyurethane foam; wherein the mixing ratio of streams (A), (B) and (C) in step (a1) is different from the mixing ratio of streams (A), (B) and (C) in step (b1), the amount of stream (C) may be zero either in step (a1) or in step (b1), and in case the amount of stream (C) is not zero in step (a1) or (b1), the amount of either stream (A) or (B) may be zero. (A) a first stream comprising at least one isocyanate reactive compound, (B) a second stream comprising at least one organic polyisocyanate, and (C) a third stream comprising at least one compound selected from isocyanate reactive compounds, organic polyisocyanates, catalysts, blowing agents, chain extenders, stabilizers, crosslinkers, flame retardants, and additives, wherein stream (C) is different from both streams (A) and (B); (a) producing at least one first article by (a1) providing a first polyurethane reaction mixture in a mixing device (MD) by mixing at least streams (A), (B) and (C); (a2) injecting the first polyurethane reaction mixture provided in step (a1) into a cavity of the at least one first article and forming the thermally insulating polyurethane foam; and (a1) providing a first polyurethane reaction mixture in a mixing device (MD) by mixing at least streams (A), (B) and (C); (a2) injecting the first polyurethane reaction mixture provided in step (a1) into a cavity of the at least one first article and forming the thermally insulating polyurethane foam; and (b) producing at least one second article by (b1) providing a second polyurethane reaction mixture in the mixing device (MD) by mixing at least streams (A), (B) and (C); (b2) injecting the second polyurethane reaction mixture provided in step (b1) into a cavity of the at least one second article and forming the thermally insulating polyurethane foam; (b1) providing a second polyurethane reaction mixture in the mixing device (MD) by mixing at least streams (A), (B) and (C); (b2) injecting the second polyurethane reaction mixture provided in step (b1) into a cavity of the at least one second article and forming the thermally insulating polyurethane foam; the mixing ratio of streams (A), (B) and (C) in step (a1) is different from the mixing ratio of streams (A), (B) and (C) in step (b1), the amount of stream (C) may be zero either in step (a1) or in step (b1), and in case the amount of stream (C) is not zero in step (a1) or (b1), the amount of either stream (A) or (B) may be zero. <EOS>