You don't need cotton with this unit. At first I was packing lightly and there was too much air. I had just had a conversation with my lhs owner about spacers he is using in the Pax, so that was the first thing that came to mind when I needed to pack it tighter. As is turns out, after talking to SliM and THR, it doesn't need to be full...it just needs to be tightly packed. You could loosely pack a very small load with a spacer like cotton and it still wouldn't work its best...it likes a tight pack. But now we have choices...pack it without cotton and use the reclaim when cleaning your pieces, or use cotton and have a clean unit with no reclaim. But the most commonly used spacer for these types of situations are the oil pads that people are using in the Plenty and now the Pax...I have no idea what they are made of.
This unit happened to get into my hands right when I started doing some modifications for the first time, so that's just the mode I'm in right now. So I'm sorry if my playing around lead some of you to believe it was necessary to enjoy the unit...that couldn't be further from the truth...I have found it to work quite well as intended. I'm just really enjoying playing around with cotton and it's oil applications (I've never used cotton like this before) and will be using it with other vapes as well. I get the apprehension as I had it too a while ago, but Vitolo's been comfy with it for years, and that's good enough for me to play around.
tl;dr -- you don't need cotton...but I am having fun using it!