The fire retardance properties of rigid, biosourced phenolic foams derived from tannins, which are novel, environment-friendly thermal insulators, are essential before the latter can be applied to the building sector. In this work, tannin-based foams prepared from new formulations and using different foaming methods were investigated by thermo-gravimetric analysis (TGA), cone calorimetry, and pyrolysis combustion flow calorimeter (PCFC). It was found that the flammability strongly depends on the formulation, so that tannin foams perform very differently depending on the presence of surfactant and plasticiser and, more importantly, on their initial water content. Moreover, a good correlation was observed between TGA and PCFC results. Nevertheless, due to their highly resistant phenolic, crosslinked, polymer network, all materials released a quite low amount of hydrocarbon fuel during thermal decomposition, leading to low heat release rates and high ignition times, and thus providing very good fire retardance properties. Based on the above, the foam presenting the highest fire retardance was identified, confirming our conclusions about the role of the ingredients in the formulation. (C) 2018 Elsevier Ltd. All rights reserved.