As stated, it's a wire, and not a spring. You don't have to use TMJ to get a quality foam. PUI is a good foam, as well as anything that Legendary sells. Legendary has great YouTube videos on how to do your seats as well . I think those wires also ring to the seat springs , if my memory serves me correctly.
1969 x-77 Z/28 orange/ white stripes, named by my daughter "Clementine ", M-22 close ratio, 4:10 12 bolt, CE 302. Hugger orange with white stripes. White standard interior. Restoration complete May 2018