69 fb back seat reupholster

In my experience, the original burlap had wires in the weave. Seat construction was 'S' springs in one direction and these wires crossing in the other direction. I think the wires helped spread the load more evenly across multiple springs and/or prevent the filler from sinking through the springs.
I did consider off the shelf burlap but found it had an odor. Soooo I ordered the correct material from Legendary. mo money
I honestly don't know how to go about reproducing bench seat filler without the OEM as a guide. Trial and error I guess. Good luck with it.