A forming tube for making filter bags of tetrahedral shape for infusion products including a forming element, which is elongate and hollow, which defines a longitudinal axis and which has a first opening through which the product enters in the forming element, a second opening through which the product leaves from the forming element to be dosed inside a filter bag being formed, and an inner through cavity which connects the first opening to the second opening and inside of which flows the infusion product. The forming element includes a main body substantially tubular including the first opening and a forming end including the second opening and mobile in rotation with respect to the main body about the longitudinal axis.