Method for producing an insulator for gas insulated switchgear by injection molding a thermoplastic resin, the method including: a filling step of filling a cavity of a mold (1, 2) with molten thermoplastic resin and a packing step of packing the thermoplastic resin in the mold (1, 2) under controlled pressure, wherein the molten thermoplastic resin is introduced into the cavity via at least a first inlet opening group, characterized in that the molten thermoplastic resin is introduced into the cavity via at least the first inlet opening group and a second inlet opening group, the packing step includes in this sequence: a first packing sub-process step, during which at a predetermined time t 0 a first pressure of the first inlet opening group is reduced relative to a second pressure of the second inlet opening group, so that the first pressure is lower than the second pressure; and a second packing sub-process step, during which at a predetermined time t 1 which is delayed in time relative to the predetermined time t 0, the second pressure of the second inlet opening group is reduced relative to the first pressure of the first inlet opening group, so that the first pressure is higher than the second pressure; wherein the sequence of the first packing sub-process step and the second packing sub-process step is repeated at further predetermined times t x, wherein each subsequent sequence is delayed in time relative to the respective previous sequence. a filling step of filling a cavity of a mold (1, 2) with molten thermoplastic resin and a packing step of packing the thermoplastic resin in the mold (1, 2) under controlled pressure, wherein the molten thermoplastic resin is introduced into the cavity via at least a first inlet opening group, characterized in that the molten thermoplastic resin is introduced into the cavity via at least the first inlet opening group and a second inlet opening group, the packing step includes in this sequence: a first packing sub-process step, during which at a predetermined time t 0 a first pressure of the first inlet opening group is reduced relative to a second pressure of the second inlet opening group, so that the first pressure is lower than the second pressure; and a second packing sub-process step, during which at a predetermined time t 1 which is delayed in time relative to the predetermined time t 0, the second pressure of the second inlet opening group is reduced relative to the first pressure of the first inlet opening group, so that the first pressure is higher than the second pressure; wherein the sequence of the first packing sub-process step and the second packing sub-process step is repeated at further predetermined times t x, wherein each subsequent sequence is delayed in time relative to the respective previous sequence. a first packing sub-process step, during which at a predetermined time t 0 a first pressure of the first inlet opening group is reduced relative to a second pressure of the second inlet opening group, so that the first pressure is lower than the second pressure; and a second packing sub-process step, during which at a predetermined time t 1 which is delayed in time relative to the predetermined time t 0, the second pressure of the second inlet opening group is reduced relative to the first pressure of the first inlet opening group, so that the first pressure is higher than the second pressure; wherein the sequence of the first packing sub-process step and the second packing sub-process step is repeated at further predetermined times t x, wherein each subsequent sequence is delayed in time relative to the respective previous sequence.