Membrane traffic occurs by vesicular transport between successive compartments of the secretory pathway. Coat complexes function to collect cargo from donor membranes and deform them to generate transport vesicles with a diameter of 60-80 nm.
References
Palmer KJ, Stephens DJ. Biogenesis of ER-to-Golgi transport carriers: complex roles of COPII in ER export. Trends Cell Biol. 2004 Feb;14(2):57-61. PMID: #15106609#