For the insertion process in all simulations the particles were injected from the top of the inlet. The insertion durations of the sequential and simultaneous injection scenarios are 14 M 𝛥𝑡 and 7 M 𝛥𝑡, respectively. When the extruder is empty in the initial phase of the simulation, the particles are pushed from one end of the extruder to the other end, through the twin-screw in about 8 M 𝛥𝑡. At around 10 M 𝛥𝑡, the foremost particles filled the extruder outlet and passed through the first bend (in the recirculation circuit) under the action of the pushing force. Therefore, we start the subsequent analysis of the microstructure of the extruded filaments at 10 M 𝛥𝑡 for all the simulation cases. In Fig. , we show the porosity of the microstructures at the outlet of the extruder (more precisely at location "Sample 1" shown Fig. ) with four groups of different material properties under the two injection scenarios (sequential and simultaneous). We can see in Fig. a clear periodic trend of progressive convergence, when the sequential injection is used. At around 10-14 M 𝛥𝑡, only BC particles are present in the microstructure. Then, the first inserted AM particles, which are for the moment not well mixed with BC, are rapidly pushed into the outlet. In addition, the packing density of particles is high. These two aspects may induce that the porosity of the microstructure drops to its lowest point at 𝑡 ≈ 20 𝑀 𝛥𝑡. After 21-23 M 𝛥𝑡, AM and BC particles mix better. Simulations of the four formulations show a trend towards stabilisation after about 30 M 𝛥𝑡, with the peaks and troughs of their porosities gradually narrowing towards a mean value.