A batch processing method was used to fabricate foams comprising of a blend of poly(lactic acid) (PLA) and Novatein, a protein-based thermoplastic. Various compositions of Novatein/PLA were prepared with and without a compatibilizer, PLA grafted with itaconic anhydride (PLA-g-IA). These were foamed at varying temperatures above the material’s Tg (80 – 160 °C). This batch foaming technique has successfully been implemented to foam both semi-crystalline and amorphous PLA using an environmentally benign blowing agent, subcritical CO2, however, batch foaming semi-crystalline Novatein is more difficult due to the constraining effects of the nature of the material. Pure Novatein cannot form a cellular structure at a foaming temperature of 80 °C, however in a blend with 50 wt. % of PLA, microcells formed with smaller cell sizes (3.36 µm) and higher cell density (8.44 x 1021 cells/cm3) compared to pure PLA and blends with higher amounts of PLA. The incorporation of 50 wt. % Novatein in PLA increased the crystallinity of the blend and the matrix stiffness of Novatein was high enough to restrain cell coalescence and cell collapse. Furthermore, the introduction of a crystalline phase from Novatein has created additional interfacial area for nucleation (interface between crystalline and amorphous phases). At a foaming temperature of 140 °C, NTP30-PLA70 showed a unique interconnected porous morphology with a pore size of 3.29 µm and cell density of 6.72 x1022 which can be attributed to the CO2-induced plasticization effect. Foaming of multi-phase systems offers a great opportunity to enhance the properties of porous materials, however, controlling the foaming process can be challenging. The outcome of this study can lead to a wider understanding about the foaming process and resulting morphologies of semi-crystalline and amorphous polymer blends.