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Tannin-based rigid foams are new cellular materials mainly based on chemicals of natural origin,especially bark extracts andfurfuryl alcohol.These porous materials can be used as such for thermal insulation and as sandwich core materials.Their outstanding chemical and fire resistance,self-extinguishing character as well as absence of harmful smokes when exposed to flame,are advantageous properties making tannin foams able to compete with commercial synthetic phenolic foams.Moreover,they release almost no formaldehyde,therefore they may have in-house applications.The introduction of additives like nanoclay filler is expected to have two possible effects: (a) easier germination of bubbles,hence production of more,smaller cells; (b) increase of viscosity of the liquid precursor before foaming,hence production of thicker cell walls.But the results show that when nanoclays were used as additives at different levels,there is no change of the apparent density and porosity,so nanoclays do not provide additional nucleation sites in the present tannin-based composition.Given that thecell morphology only depends on the amount of blowing agent.