I was designing rings earlier this week and had to do some testing on this. I didn't design the rings to come to a full circle but instead just a 3/4 circle that went around my finger. This made it much easier to fit on different areas of different fingers as it was able to flex a little bit. At first I was using 2 layers (a ring which was .95mm thick) but I found that if I bent the piece too far it wouldn't bend back. I then tried a 4 layer thick print (1.9mm) and found that it was too stiff or would break if I bent it too much. The best option for me was a 1.3mm thick piece (3 layers) as it was flexible enough to fit around my finger, but it was thick enough where it wanted to retain its original shape. Tl;dr - anything between 1 and 3 layers thick will bend easily (.3mm settings). 1 is floppy and can bend so far that it wont retain original shape. 2 is not floppy but can still be bent to the point where it won't retain its shape. 3 works the best for me as it can bend yet it will come back to its original shape.
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