If a number of studies have been made to evaluate the influence of cigarette paper porosity on CO formation/diffusion, it was still needed to evaluate, on a practical basis, the influence of each of the paper parameters on CO formation, and CO loss by diffusion and dilution. In this study, we have measured the influence of cigarette paper basis weight, and the influence of real porosity versus permeability (impact of pinholes) on CO formation, diffusion and dilution. We found that when basis weight is increasing, the CO formation is increased. But, at low basis weight, less CO is lost by diffusion. The lowest CO delivery will then depend on the balance between lowest grammage and highest possible diffusion coefficient. For porosity, we found that, when increasing the measured permeability up to 50-60 CORESTA, both dilution and diffusion through the cigarette paper increase with high reductions on CO and CO/tar. Above, the reduction of CO is only due to the increase of dilution through the cigarette paper.