TOBACCO-SMOKE FILTERS

摘要

A tobacco-smoke filter comprises a plug of filter material of which a transverse cross section is impervious to the passage of smoke except for a minor proportion of the area of that cross section which forms a smokeaccelerating orifice, the said plug being enclosed by an envelope permitting ingress of air into a region of the plug downstream of the orifice. The cross section may be impervious because of the presence of a barrier diaphragm of impervious material. Thus an annular groove may be provided in the plug at the said cross section and may be filled with, or have its walls coated with, an impervious material. Alternatively the said cross section may be impervious by reason of the closure of interstices in the filter material by the local application of heat thereto.