Abstract: Secondary smoke is harmful to passive smokers. A filter sleeve (1) comprises a sleeve (10) with a downstream portion (11) adapted for receiving inhale smoke into an inhalation flow path (13), an upstream portion (12) adapted for inhalation of said inhale smoke and for receiving exhale smoke into an exhalation flow path (14), filter means (15) provided along said exhalation flow path (14), and means (16) for checking reverse flow of ambient air through said exhalation flow path (14). A filter sheath (3) is adapted for overlaying a significant expanse of the sidestream smoke emission areas of a rod of smokable material (7), said filter sheath (3) is sufficiently porous and significantly unimpaired by combustion.