After using these for a few days, here is how I think that they work and how they work best. My goal was to see if I could use one of the wool liners to prevent the body of the fitted dipe from getting wet. It is possible if all these conditions are met:
1. The wool liner is placed under a soaker that is pretty substantial (for my heavy wetting son, that means a good sized soaker and 4-5 layers of hemp fleece).
2. The wool liner is slightly larger than the soaker, and the soaker snaps into the back. If the soaker snaps into the front, you can't get the wool liner all the way underneath it, and then moisture will will from the very top of the soaker onto the body of the diaper. I also didn't have good luck with a lay-in soaker-- it seems that (at least for my active baby) that the soaker can shift if not snapped in and compress against the body of the diaper and then moisture will wick onto the body of the diaper.
3. The diaper has to have a good, snug fit against baby's body, especially in front (I have a boy; this might be different for a girl). If the diaper not right up against baby's skin, then when baby pees it goes everywhere (not just right into the soaker) and the whole system is shot.
For those who are curious about the wetness factor-- have you experienced the phenomenon with hemp where it doesn't really feel damp, but you know it's really wet (as opposed to sopping wet when you remove the dipe)? What seems to happen when hemp works well (and is most absorbent) is that the fibers suck up more of the moisture rather than laying right on top of it). Although the fiber surface of the fabric can absorb, underneath the surface is the fiber core microstructure (which looks like millions of tiny spong-like tubes under a microscope). (see picks and more explanation from FuzDaddy here: http://www.fuzbaby.com/articles/art-absorb.htm
My theory is the that wool liner forces the moisture into the fiber core of the soaker (hemp/cotton fleece in my experience), which means there is less moisture on the surface of the fabric. When I take off the fitted diaper that has had the wool liner underneath the soaker, it doesn't feel like I could wring out the urine from it (as it would if I hadn't used the liner). It is that dry-damp feeling that I think comes from the fabric absorbing into the core microstructure as opposed to the fabric surface.