A typical GUV fusion event is shown in Fig. . The contact area between two neighbouring GUVs increases without any observable lipid mixing between the two GUVs. A full fusion pore then opens and the interior lumens of the GUVs mix. This is followed by reconfiguration of the combined GUVs into a single spherical vesicle, where the red and green lipid probes become evenly mixed throughout the membrane by lateral diffusion. Lipid nanotubes that can be seen in the two initial vesicles are conserved within the lumen of the initial fused GUV. However, these tubes disappeared within 2 min of the fusion event, likely retracting into the GUV membrane as the lipid mixture re-equilibrates.