To give some volume to a mattress-cover, in the past multiple layers of fabric were sewn together by hand (pitted), or machine. You can achieve the same effect with this 3D knitting, with a filling thread between top and bottom knit.
In this sample, I want to use the technique for another purpose: acoustic wall coverings. The development is not finished, because the use of fire-retardant material is obligatory. A filling thread, a strong frizzy polyamide, is not (as yet) available in a fire-retardant quality.
In circular knitting the needles/pins are set in a circle. Circular knitting is possible with various bobbins (cones) for yarn supply, all depending on the diameter of the knit. Known applications of circular knitting are tights and T-shirts.