When the MWCNT content is lower than 0.75 wt% (Fig. S6a–c), a majority of MWCNTs are observed at the interface of the PLA/PCL blend. However, some MWCNTs are also found in PCL phase when the MWCNT content is higher than 0.75 wt%, as shown in Fig. S6d–f. This is because the space of the interface is limited and the interface cannot accommodate such a large amount of MWCNTs. As a result, some MWCNTs crossed the interface and entered into the favorable PCL phase at high MWCNT content. The determined percolation threshold is ca. 0.025 wt%, which is much lower than 0.75 wt%. Therefore, the calculation of percolation threshold from Fig. 5 is reasonable. Moreover, the increase of MWCNTs in the continuous PCL phase leads to a further increase in AC conductivities of the mixture, as shown in Fig. 5.