Headbox for manufacturing a substrate

A headbox including a machine direction, a cross direction, and a height direction, the headbox comprising at least one flow section, the at least one flow section comprising:

• a bottom surface spaced from a top surface;
• and
• wherein the at least one flow section comprises in order in the machine direction:
• i) a constriction zone;
• ii) a slice zone;
• iii) an expansion zone;
• and
• iv) a formation zone,
• wherein the constriction zone has an initial height (ti) and the height constricts along the machine direction to a slice height (ts);
• wherein in the slice zone is in fluid communication with a downstream end of the constriction zone and has a slice length (ls) in the machine direction and a height equal to the slice height (ts) over the slice length (ls);
• wherein the expansion zone is in fluid communication with a downstream end of the slice zone and has a beginning height equal to the slice height (ts) and the height expands along the machine direction to an expansion height (t1);
• and
• wherein the formation zone is in fluid communication with a downstream end of the expansion zone and has a beginning height equal to the expansion height (t1) and the height constricts along the machine direction to a formation height (t2).