A method for producing bags containing fibre material, comprising the steps of - providing portions of fibre material and moving them along a predetermined path; - feeding each portion of fibre material to respective containment and compaction elements of a first transfer conveyor; - feeding an ordered succession of bags containing respective portions of fibre material to respective supporting elements of a second transfer conveyor; - transferring the portions of fibre material from the containment and compaction elements of the first transfer conveyor into respective housings of a third transfer conveyor; - transferring the portions of fibre material from the housings of the third transfer conveyor inside respective containment bags carried by supporting elements of the second transfer conveyor; - transferring the containment bags housing respective portions of fibre material from the respective supporting elements of the second transfer conveyor to a fourth transfer conveyor; - moving in succession the bags housing respective portions of fibre material to a folding unit at which the bags are closed; characterized in that said step of providing portions of fibre material is realized forming at least one continuous layer of fibre material and separating in succession portions of fibre material from the continuous layer, and in that the method comprises the further step of adding predetermined quantities of fibre material, using a supplemental feeding device, to the portions of fibre material; the amount of the predetermined quantity of fibre material being established by at least one device (28, 38) for weighing the portions of fibre material. - providing portions of fibre material and moving them along a predetermined path; - feeding each portion of fibre material to respective containment and compaction elements of a first transfer conveyor; - feeding an ordered succession of bags containing respective portions of fibre material to respective supporting elements of a second transfer conveyor; - transferring the portions of fibre material from the containment and compaction elements of the first transfer conveyor into respective housings of a third transfer conveyor; - transferring the portions of fibre material from the housings of the third transfer conveyor inside respective containment bags carried by supporting elements of the second transfer conveyor; - transferring the containment bags housing respective portions of fibre material from the respective supporting elements of the second transfer conveyor to a fourth transfer conveyor; - moving in succession the bags housing respective portions of fibre material to a folding unit at which the bags are closed; characterized in that said step of providing portions of fibre material is realized forming at least one continuous layer of fibre material and separating in succession portions of fibre material from the continuous layer, and in that the method comprises the further step of adding predetermined quantities of fibre material, using a supplemental feeding device, to the portions of fibre material; the amount of the predetermined quantity of fibre material being established by at least one device (28, 38) for weighing the portions of fibre material.