For comparison, a series of PLA/PCL/MWCNTs (PLA/PCL = 50/50, w/w) composites were prepared by simultaneously mixing all the three components (see Supporting Information S1). At a fixed PLA/PCL weight ratio of 50/50, these composites also contained a co-continuous phase structure with MWCNTs selectively located in the PCL phase. The PLA/PCL/MWCNTs composites displayed a lower percolation threshold (0.97 wt%) (see Supporting Information S4 and Fig. S5) compared with PLA/MWCNTs composites (pc = 1.34 wt%) or PCL/MWCNTs composites (pc > 5.0 wt%). However, this value was still much higher than that of the PLA/MWCNTs/PCL composites because of the controllable distribution of MWCNTs at a continuous interface of the co-continuous PLA/PCL blend and the build-up of a percolated MWCNTs network at an ultralow MWCNTs concentration (0.025 wt%) at the continuous interface in the PLA/MWCNTs/PCL composites. Clearly, the increase of MWCNT content in the PLA/PCL blend may have some influence on the interfacial distribution of MWCNTs. In Fig. S6, we present a series of TEM images to show the dependence of the location of MWCNTs on the MWCNT content. 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.