A method for producing a foamable embryo having a volume V final using injection moulding comprising the steps of: - providing a plastisol; - providing an injector unit for injection moulding comprising a barrel with a nozzle and a control unit adapted to control the back pressure P back inside the barrel and to maintain said pressure above a critical foaming pressure; - providing a mould comprising an injector port, a force exerting means, a first and a second mould half forming a mould cavity with a cavity volume, wherein the mould halves are moveable in relation to each other to vary the cavity volume, wherein the mould is provided in a cold state having a cavity volume of V min and wherein the force exerting means exerts a controlled maintained clamping force F set on the mould cavity creating a pressure P 4 inside the mould; - connecting the injector port of the mould to the nozzle of the injector unit; - adding the plastisol to the injector unit; - preparing a shot volume V shot of hot melt of the plastisol in the injector unit; - injecting the hot melt into the cold mould cavity of volume V min ; - continuing injecting the hot melt into the mould cavity creating a cavity pressure P cavity equal to or higher than the clamping pressure P 4 forcing the mould to expand so that it can receive the shot volume V shot ; - allowing the injected hot melt to cool in order to form an embryo whereby the volume of the embryo contracts during the controlled maintained clamping force F set allowing the mould cavity to contract reducing the risk of a pressure drop in the cavity causing foaming in the formed embryo; and - opening the mould and removing the formed injected moulded embryo. - providing a plastisol; - providing an injector unit for injection moulding comprising a barrel with a nozzle and a control unit adapted to control the back pressure P back inside the barrel and to maintain said pressure above a critical foaming pressure; - providing a mould comprising an injector port, a force exerting means, a first and a second mould half forming a mould cavity with a cavity volume, wherein the mould halves are moveable in relation to each other to vary the cavity volume, wherein the mould is provided in a cold state having a cavity volume of V min and wherein the force exerting means exerts a controlled maintained clamping force F set on the mould cavity creating a pressure P 4 inside the mould; - connecting the injector port of the mould to the nozzle of the injector unit; - adding the plastisol to the injector unit; - preparing a shot volume V shot of hot melt of the plastisol in the injector unit; - injecting the hot melt into the cold mould cavity of volume V min ; - continuing injecting the hot melt into the mould cavity creating a cavity pressure P cavity equal to or higher than the clamping pressure P 4 forcing the mould to expand so that it can receive the shot volume V shot ; - allowing the injected hot melt to cool in order to form an embryo whereby the volume of the embryo contracts during the controlled maintained clamping force F set allowing the mould cavity to contract reducing the risk of a pressure drop in the cavity causing foaming in the formed embryo; and - opening the mould and removing the formed injected moulded embryo. <EOS>