Hey Smokey,
As a maker of pouches, I can tell you that the results I've had in trying to come up with the perfect lining to keep tobacco fresh has been very mixed and depends on a few variables. The main variable, however, in how long tobacco will stay fresh in a pouch, is the tobacco itself. Are you putting in different tobaccos? or are you using just one, mainstay tobacco that keeps drying out? If so, which tobacco is that?
I have found that the best lining to keep tobacco freshest, the longest, is a clear, thin, vinyl that I actually attach to the leather itself. It will keep most tobaccos moist for at least a few days. I say, most, because some tobaccos, no matter what you do, will just dry out no matter what, unless you smoke them in a day's time.
In general, Aros, of course, seem to stay "freshest" the longest (I'm talking about decent quality aromatics, not the super goopy kind, which never dry out). Burleys and straight Virginias seem to dry out the quickest. And many English blends will have mixed results, depending on the blender and the cut, (McClelland blends seem to do really well--esp. any of the Frog Morton blends, Dunhill blends seem to dry out if you just look at them, but, ribbon cut blends, in general, don't do all that well because the cut itself creates a lot of "air" in the blend).
In other words, how moist a tobacco will stay in a pouch has less to do with the pouch and more to do with how moist the tobacco comes in its own tin. The more moist in the tin, the longer it will last in the pouch.
I often advise to put more tobacco (at least an ounce) in a pouch, so the more "space" is filled up in a pouch by tobacco (and not by air--which is the real enemy here). The more tobacco, in general, you fill, the more it will "stick together" and feed off its own moisture. Just remember to fill your pouch with more tobacco as you smoke so there are no dips in the pouch's humidity level. An ounce or so, of say, ribbon tobacco, might seem bulky in a small, roll up pouch, but, if you press down on it and compact it (just like it comes in many cans) it will help to keep it fresh a bit longer.
So far, I have not found a pouch/liner combo (either of my own making or someone else's) that will keep tobacco fresh forever, but, if you're carrying around tobacco that you want to stay fresh forever, you're probably not smoking enough of it to justify carrying it around.
P.S. I have also just started making leather roll up pouches with all leather linings. This was how tobacco pouches were made in the days of the Civil War. So far, the results are pretty good, but, again, unless you're walking around with a mason jar, your tobacco is really the deciding factor in how fresh it will stay for how long. Hope that helps.
