Cigarette filter

A cigarette comprising a tobacco rod and a filter rod for filtering mainstream smoke from the tobacco rod, said filter rod having a tobacco rod end and a mouth end, said filter rod being made of a fibrous filter material overwrapped with a plug wrap, said filter rod having a core region extending longitudinally of the filter rod and an annular region surrounding said core region, a tipping paper connecting said tobacco rod with said filter rod, air dilution means extending into the fibrous filter material for admitting ambient diluting air into said core region of the filter rod such that the flow of dilution air is concentrated in said core region and the flow of mainstream smoke is concentrated in said annular region, said air dilution means comprising a plurality of holes located adjacent the tobacco rod end of the filter rod and extending through the tipping paper and plug wrap and into the fibrous filter material of the filter rod to a substantial depth sufficient to concentrate substantially all of the flow of diluting air in the core region of the filter rod, said filter rod being free of other air dilution flows into said filter rod so that the flow of mainstream smoke from the tobacco rod end of the filter rod through the annular region to the mouth end of the filter rod is substantially undiluted by air from the holes and substantially all dilution air admitted to the filter rod though the holes flows to the mouth end of the filter rod through the core region of the filter rod.