The invention provides inorganic fibers based on calcium sulfate dihydrate or calcium sulfate aluminate hydrate (or their dehydration products), wherein the ratio of average length to diameter of the fibers is more than 100:1 and the length of the fibers is at least 0.2 mm; preferably the ratio of average length to diameter is 300-800:1, and the length is 0.5-6 mm.
