By combining two measures, namely by using rock wool fibers with a particularly low fiber thickness, and by adding an avivage agent with an unusually high viscosity, it is possible to needle a rock wool felt, without adding any other fibers, to produce a needle felt with high strength and good bendability. If the needle felt is subsequently relaxed with heat treatment, and the avivage agent is also expelled during this treatment, the needle felt is then available as a pure rock wool needle felt, free of any organic additives.