A filling unit for filling containing elements of single-use capsules with a dose of product for extraction or infusion beverages, comprising: - a line for transporting the containing elements extending along a first movement path and provided with a plurality of supporting seats for the containing elements arranged in succession along the first movement path; - a station for filling the above-mentioned containing elements with a dose of product; characterised in that the filling station comprises: - at least a first containing seat designed to receive a dose of product; - a substation for forming the dose inside the at least one first containing seat located at a region for forming the dose and provided with a device for releasing within the at least one first containing seat a predetermined quantity of product which defines the dose, the release device comprising a hopper and at least one first rotary element (40a; 40b), associated with the hopper and having a helical profile which extends between a first end and a second end, the at least one rotary element (40a; 40b) being configured for rotating about a respective axis of rotation (X4; X5), in such a way that the first end adopts an angular position variable over time around the respective axis (X4; X5) of rotation, the respective axis (X4; X5) of rotation being stationary with respect to the hopper and positioned angularly inclined to a horizontal plane, to create a feed flow of product, from the second end to the first end, which intercepts the at least one first containing seat and to release the product inside the at least one first containing seat; - at least a second containing seat designed to receive the dose of product from the at least one first containing seat; - a substation for transferring the dose of product from the at least one first containing seat to the at least one second containing seat; - devices for moving the at least one first containing seat between the forming substation and the transfer substation and vice versa; - a substation for releasing the dose of product from the at least one second containing seat to a containing element transported by the transport line; - further moving devices for moving the at least one second containing seat between the transfer substation and the release substation, and vice versa; - a drive and control unit, operatively connected to the at least one rotary element (40a, 40b) and configured to rotate it at a speed of rotation variable as a function of the angular position of the first end of the at least one rotary element (40a, 40b). - a line for transporting the containing elements extending along a first movement path and provided with a plurality of supporting seats for the containing elements arranged in succession along the first movement path; - a station for filling the above-mentioned containing elements with a dose of product; - at least a first containing seat designed to receive a dose of product; - a substation for forming the dose inside the at least one first containing seat located at a region for forming the dose and provided with a device for releasing within the at least one first containing seat a predetermined quantity of product which defines the dose, the release device comprising a hopper and at least one first rotary element (40a; 40b), associated with the hopper and having a helical profile which extends between a first end and a second end, the at least one rotary element (40a; 40b) being configured for rotating about a respective axis of rotation (X4; X5), in such a way that the first end adopts an angular position variable over time around the respective axis (X4; X5) of rotation, the respective axis (X4; X5) of rotation being stationary with respect to the hopper and positioned angularly inclined to a horizontal plane, to create a feed flow of product, from the second end to the first end, which intercepts the at least one first containing seat and to release the product inside the at least one first containing seat; - at least a second containing seat designed to receive the dose of product from the at least one first containing seat; - a substation for transferring the dose of product from the at least one first containing seat to the at least one second containing seat; - devices for moving the at least one first containing seat between the forming substation and the transfer substation and vice versa; - a substation for releasing the dose of product from the at least one second containing seat to a containing element transported by the transport line; - further moving devices for moving the at least one second containing seat between the transfer substation and the release substation, and vice versa; - a drive and control unit, operatively connected to the at least one rotary element (40a, 40b) and configured to rotate it at a speed of rotation variable as a function of the angular position of the first end of the at least one rotary element (40a, 40b).