The development of biopolymers for food-packaging applications implies ecofriendly character to specific industrial requirements as low-cost and good mechanical, thermal and barrier properties. Polylactide (PLA) is today the most used a biobased and biodegradable polymer due to its process ability and good mechanical properties [1]. As one of the major challenges for high performance PLA packaging at a large scale is the improvement of its gas barrier properties, the tailoring of the PLA microstructure. Methods, such as thermal crystallization [2,3] and drawing [4] have been strongly investigated in the recent years. New strategies are actually studied to obtained stronger effects. One of them consists in the geometrical confinement of the polymer at the molecular scale using the layer-multiplying co-extrusion process combined eventually with annealing processes to create nanometric thickness layers. This technology is environmentally friendly and health secured and has already proved its efficiency to improve the gas barrier properties in case of other polymers [5]. In this work we propose to design multi-layer coextruded PLA to analyze the relationships existing between its microstructure, amorphous phase mobility and the resulting gas barrier properties. (1) Domenek S, Ducruet V. Characteristics and applications of polylactide, in “Biodegradable and biobased polymers: Environmental and biomedical applications”, Kalila S, Averous L, eds, Scrivener Publishing.2015,171-224. (2) Guinault, A.; Sollogoub, C.; Ducruet, V.; Domenek, S. Eur. Polym. J. 2012, 48, 779–788. (3) Cocca, M.; Lorenzo, M. L. D.; Malinconico, M.; Frezza, V. Eur. Polym. J. 2011, 47, 1073–1080. (4) Delpouve, N.; Stoclet, G.; Saiter, A.; Dargent, E.; Marais, S. J. Phys. Chem. B 2012, 116, 4615–4625. (5) Carr, J. M.; Mackey, M.; Flandin, L.; Hiltner, A.; Baer, E. Polymer 2013, 54, 1679–1690.