The present invention relates to a thermal insulation device for a turbine generator including a turbine (30) of which the wheel (66) is rotated by a hot fluid flowing between a fluid inlet (32, 32') and a fluid outlet (34, 34'), and an electricity generator (38) coupled to said wheel by a linking shaft (36). According to the invention, a polymer heat shield is inserted at the junction between the turbine (30) and the generator (38).