Foams or vegetable composites can represent solutions to reduce the environmental impact in the building sector by decreasing the use of non-renewable materials. Some composite foams are employed as insulating material due to their low porosity which can be induced using surfactants allowing the foaming during the mixing step. Generally, the composition of foams includes exclusively mineral resources without vegetable part. This study aims to investigate the influence of two surfactants, the petrosourced foaming agent (PFA) Betomouss® and the biobased decyl α/β D-xylose ether (C10Xyl), on the foaming, stability, consistency, mechanical and thermal performances of a plant-based composite foam made of gypsum, earth and flax shives. The petrosourced surfactant decreases from 10 to 21 % more the dry density of the composite than the biosourced. This last generates larger air void bubbles than the petrosourced. The results have also shown that the addition of surfactant (biosourced or petrosourced) improves the fluidity of the plant-based composite in increasing the spreading diameter from 34.8 up to 50.8 % according to the surfactant concentration. The air void concentration is doubled inducing a thermal conductivity from 0.078 to 0.097 W m−1 K−1 in place of 0.147 W m−1 K−1 for the mix without foaming agent and a good thermal inertia with a time lag around 12 h and a decrement factor around 0.045, in considering a 240 mm depth material.