I have the same machine that you have (Janome 204D) and I've found that 3 layers of hemp fleece or french terry is about the limit (more of hemp jersey). However, I do make diapers with 6 layers of hemp using my serger. I make the soaker 3 layers and then sew it to one of the body layers using my conventional machine, then I serge together 3 body layers...and there we have 6 layers of hemp. If I want, I can make it 9 layers with an external soaker laid inside the diaper when I put it on. They drying time for the diaper is FOREVER, but that's okay with me. If you want quick-dry, you don't want more than 3 layers anyway. You can make your soaker external - either lay in, snap in, or sewn in on one end, and then you have better drying time without compromising absorbency. I just hate having to assemble diapers so I make mine with internal soakers and then practice patience when drying them. In fact, I've discovered that when I dry them in the dryer, if I put a large bath towel that's dry in with the wet diapers, it significantly speeds drying time. Usually I line dry them, though, so it doesn't matter.