This project uses both knitting and crochet. (The knitting needle is size 3; for some reason I don’t seem to be able to add both a needle size and a hook size…)
To be sure that the central area was directionless and seamless, I used an intrinsic-twist Mobius band. (There is not currently a known seamless/directionless crochet foundation stitch, and whether one exists is an open problem at the moment.) Then I transfered to a front/back symmetric crochet stitch for one round, and then continued in left-hand/right-hand insertion single crochet for the remainder. This assured that the entire object is as symmetric as possible (front/back and up/down in particular). Additionally, I induced negative curvature by doing two single crochets into one stitch below every 5 below-stitches.