In this paper, "green" tannin-furanic foams were prepared based on formulations free of formaldehyde and foaming agent, aiming at obtaining the best thermal insulators as possible with the highest mechanical resistance. Both of these properties are antagonistic, since low thermal conductivity requires high porosity whereas high mechanical properties require low porosity. Thus, experimental design was applied for the first time to this kind of formulations. Thanks to a limited number of experiments suggested by a rational mixture design, the experimental responses: thermal conductivity, elastic modulus and compressive strength were modelled and predicted based on the relative proportions of three main ingredients of the formulation. The results revealed that the formulations containing a high proportion of furfuryl alcohol, a moderate proportion of tannin and a low level of catalyst led to the best compromise between properties having opposed trends. Thus, optimised foams presented a thermal conductivity of 0.039 W m(-1) K(-1) and compression strength of 0.07 MPa. The reliability of the model used was successfully validated by additional tests. This proved it to be a very useful tool for developing environment-friendly tannin-furanic foams with desired features.