in fig1 aluminum strips have been applied to a commercially available highly porous paper for wrapping cigarette filters ( papierfabrik wattens gmbh , qno 27400 ), with an air permeability of 6000 cu , by performing a hot foil process . a width of the porous paper was 26 . 5 mm and a width of each aluminum strip was 1 mm . a spacing between the strips was 1 mm . filter rods for cigarettes were produced in a per se known manner from a usual industrial acetate cable measuring about 1000 m in length . fig1 shows a structure of such a filter rod comprising acetate cable 1 , wrapping paper 2 and tip layer 3 , while reference 4 denotes the aluminum strips according to the invention . cigarettes are produced by machine , using these filter rods . for comparison purposes , cigarettes were produced on a basis of the same composition in terms of filter , cigarette paper and tobacco blend , but without previous zone - wise coating of a filter wrapping paper . the cigarettes produced were smoked under standardized conditions in a smoking laboratory . with regard to cigarettes of the invention , smoke constituents of a main smoke flow had a selectively and significantly lower carbon monoxide content , as shown in table 1 . fig2 shows another embodiment according to the invention . here , with a structure of the filter rod otherwise being the same with regard to acetate cable 1 and tip layer 3 , filter wrapping paper 2 was coated with aluminum in a finely distributed form , but here aluminum layer 5 was highly porous . this kind of aluminum coating ensures that air permeability of the filter wrapping paper is sufficiently maintained so that , as also with the embodiment of fig1 sufficient air can pass laterally into the cigarette filter . for comparison purposes and to demonstrate action of the highly porous aluminum layer 5 , besides the embodiment according to the invention as shown in fig2 otherwise identical cigarette filters were produced without aluminum coating 5 on wrapping paper 2 . these filter rods were used to produce , by machine , otherwise equivalent cigarettes with and without the coating 5 . the cigarettes produced therefore differ only with regard to presence of the coating 5 . the cigarettes produced in that way , as in the case of the embodiment of fig1 were also smoked under standardized conditions in a smoking laboratory . measured smoke constituents of a main smoke flow of cigarettes of this embodiment also have a selectively and significantly lower carbon monoxide content , and therefore , have a similar effect as with the first embodiment . table 2 shows results of measurement of the same parameters as in table 1 , but in a comparison between cigarettes with a standard filter wrapping paper , and cigarettes with filter wrapping paper 2 according to the second embodiment of the invention , which is coated with a finely distributed highly porous aluminum layer 5 . clearly , the invention combines a known advantage of filter venting with an effect which is to be attributed to a metal coating . in this respect , the two embodiments show that an effect can be demonstrated , irrespective of a nature of the metal coating , as long as combination of air permeability of filter wrapping paper and metal coating of the filter wrapping paper is guaranteed . this makes it clear that the invention is not limited to the illustrated embodiments , but includes all possible combinations of the embodiments shown herein and other embodiments in accordance with combining a porous filter wrapping paper and a metal coating . a physical or chemical mechanism to which this effect is to be attributed still remains to be investigated . a possible explanation would be adsorption of carbon monoxide by the metal coating , whereas a purely catalytic action , because of a low temperature in the filter , is improbable .
a cigarette filter is surrounded by a wrapping paper , and the wrapping paper includes metal only on portion of a surface thereof , such that air can penetrate through the wrapping paper into the filter .