For improving the cleaning effect of a fibrous material in an opener (1) comprising a rotatable opener roller (2) and blades (3,4) and carding plates (5) cooperating with the peripheral surface of the roller (2), there is provided in the material drawing zone at least one separator element (13) for the air current (14) generated by the rotation of the opener roller (2). The separator element (13) penetrates with a certain angle into the air current (14) and so it allows to deviate away from the opener roller (2) a radially outermost part of the air current (14), which owing to a greater centrifugal action includes residual impurities and cotton flocks still incorporating dirt or not yet opened because they have remained clamped between the teeth of the roller clothing, whereas the radially innermost part of the air current (14), which carries cleaned fibrous material that is lighter, is conveyed towards the outlet (16) for the material. The separator element (13) may be adjustable in position.