Microbial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) bio-polyester was combined by thermoforming with Kraft lignin in order to design new advanced composite materials for packaging purpose. After assessing the compatibility of the two raw materials, the thermoformed composite sheets were investigated in order to assess the impact of the lignin fraction (between 0 and 10 wt.%) on melting and crystallization, behavior, thermo-oxidative stability, mechanical and viscoelastic properties, and permeability for oxygen and carbon dioxide. It turned out that the applied Kraft lignin is highly compatible with microbial PHBHV, and by exerting a reinforcing effect, acts as an active additive. As aspired, the gas permeability was decreased by combining PHBHV with 1 wt.% lignin; here, a reduction of permeability for oxygen by 77% and by 91% for carbon dioxide, respectively, was observed if compared to the native bio-polyester specimens. Also the low thermo-oxidation stability, a typical characteristic of pure PHBHV, was increased for the lignin-containing materials. This first report on thermoformed composite materials of microbial PHBHV and lignin suggests a new class of bio-based polymer materials to be applied for packaging of various easily perishable goods. (C) 2015 Elsevier B.V. All rights reserved.