For the interpretation of the limits we observed within the previous sections, we have designed several simplified boundaries as a multiplication of 4 log units, that can help to explain the limitations of permeability coefficients in real world examples of the time scale for permeation events (Fig. ). Hence, the first line of logPerm around -12 log units corresponds to the lowest permeation rates still measurable by single-membrane experimental methods. It is close to the practical limit of the slowest passive permeation that still results in a biologically feasible amount of e.g. highly toxic compounds permeating over a physiologically relevant amount of time. For a permeation area equal to that of an entire human intestine (30 m 2 ) and 0.1 L as a volume of the intestinal fluid, 71 only 0.25 % of a permeant will have permeated in ten days at such rate with logPerm = -12 log units.