One hypothesis for a fission pathway9 postulates that GTP hydrolysis leads to unbinding of the Sar1 amphipathic helix from the membrane, resulting in packing defects. Such defects should lead to rapid changes in membrane morphology to fill the gaps and avert the energetically unfavorable exposure of the hydrophobic lipid chains to water. To preclude simple contraction (i.e., shortening of the lipid tubule) as a path of relaxation, a separation force may be needed. Separation forces can be static, i.e. maintaining the length of the protrusion, or dynamic, i.e. actively extending the protrusion. Static separation forces, applied artificially by attachments to an EM grid, have been reported to support fission of dynamin-mediated tubular constrictions2021. In vivo, dynamic separation forces may be exerted by motor proteins and cytoskeleton, for example, by dynactin/dynein coupling to Sec23p22. Here, we observed that tubules formed by COPII were, despite their constrictions, globally rigid over several micrometer (Fig. 3b, Movie S2), demonstrating that the COPII scaffold conveys rigidity and directionality including at the necks between the bulges. The coat may thus itself act as an ‘exoskeleton', providing a static separation force between the bulges and obviating the need for cytoskeleton involvement in simple COPII budding.