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This is a modified version of the box I had printed myself, and discussed on BoardGameGeek in the thread at http://www.boardgamegeek.com/thread/755740/3d-printed-population-cube-box. I felt the original worked well, but it does have quite a tight fit between the top and the bottom, as you can see in the video. For this updated version I've slightly increased the gap between the two, which should make for an easier fit.
I had my copy of the original printed in White, Strong, and Flexible and it works well for me. The consistency of the material is slightly coarse; rubbing your finger along it feels a bit like rubbing your finger along a (hard) cotton shirt. If you want a truly smooth surface, you may want to go with the White Strong & Flexible Polished.