Cigarette filter

Claim 1

A tobacco smoke filter comprising: a. an axially extending tubular outer member having an inner surface, b. within said outer member an axially extending air permeable inner member comprising an air permeable rod of fibers which are bonded to each other at their points of contact, said inner member having an outer surface, c. at a first longitudinal position, the outer surface of the inner member being in engagement with the inner surface of the outer member over a complete circumferential ring so as substantially to preclude axial passage of the smoke between said inner and outer members at said first position, d. at a second longitudinal position, longitudinally spaced from said first position, the fibers of which the rod is comprised being formed into a portion of substantially smaller transverse cross-sectional area than the transverse cross-sectional area of said rod at said first position, the density of said rod at said second position being greater than the density of said rod at said first position, e. said rod having an intermediate outer surface between said first and second positions, at least a portion of said intermediate outer surface being spaced from and lying within, said inner surface of said outer member, cavity means defined in part by said intermediate outer surface portion and a portion of said inner surface of said outer member and being closed at least at one end by portions of said circumferential ring, and f. the area of said intermediate outer surface portion being greater than the transverse cross-sectional area of said rod at said first position.