fma wrote:This is strange... I don't see how this could happen when the filament is put on the spool; to get this problem, this would require to roll the filament *under* previous layers...
Simple - roll one turn from one end to the other, make a few turns there, then roll one turn back to the other side and roll a few turns there (making an X).
Also, what often seems to happen is, when the filament gets loose, a turn will end up with a SMALLER diameter than the turn coming immediately after it off the spool (instead of a bigger diameter). Depending on its path, it's possible for the first turn to go through the next turn, making a tangle.