As I have posted before on this forum concerning density...when I order a custom it usually is less dense than a stock unit...even though they both are at 65%. that being said I think the point that most are not taking into consideration is the fact that this is not an exact science as it has been said many times before...I really don't know all the ins and outs that go on at the factory...but I think most of the ventillation is someones conception of what 65% really means and then I assume it would be left to quality control to make that determination...I would also assume that the least experienced ventillators would be doing stock units and the pros would be producing custom units...it is also possible that when you order multiple units they are being produced by various people and that may be why some units...even though it is the same order will be somewhat different in density...Just my thoughts...If someone here knows the production procedures of the factory...and gives us a heads up about what is happenning then that would be beneficial to us all...Cheers