Halogen-free system and/or bio-based flame retardants have been tested to improve the fire behavior of bio-based polyurethane foams produced by substitution of fuel based polyols with renewable ones based on cashew nut shell liquid. Because this is a food-industry waste, it does not compete with food production as is the case with many biosourced industry products. The full substitution of polyols with bio-based ones can be successfully carried out, with the investigation of physical-mechanical properties, fire behaviour and thermal stability performances. The latters resulted to be not satisfactory achieved when using only bio-based flame retardants, hence a suitable combination of bio-based and halogen free flame retardants must be used to improve these properties.