A sheath for a smoking article, such as a filter cigarette, including an exterior sheath (5) that provides a ventilation structure which has a reduced possibility of occlusion, and which also prevents a reduction in filter efficacy when the strength of the draw on the smoking article by the consumer is increased, for example in order to overcome the effects of dilution of the smoke flow with ambient air. The sheath may be manufactured as an independent entity and then fitted to prefabricated smoking articles, or alternatively may be constructed as an integral part of the smoking article.