Restricted flow die

A coating die comprising:

• a first half;
• a second half located adjacent the first half to form a manifold and a slot between the first and second halves, wherein the slot extends from the manifold to the ends of the coating device to form an exit having an exit area defined by a slot gap height and a slot width;
• and
• means for creating a controlled predetermined pressure drop through the slot and for maintaining the pressure drop through the slot at a defined flow rate to create the desired flow rate along the slot width, wherein the creating and maintaining means comprises a porous material having an uncompressed thickness greater than the gap height of the slot, disposed in the slot between the slot exit and the manifold to compress uniformly along its width to a thickness substantially equal to the height of the slot, and having a porosity and a length selected in combination with each other to create when compressed the controlled predetermined pressure drop, wherein the size of the pores in the porous material is less than 25 .mu.m, wherein the exit pressure drop attained is at least one thousand times greater than could be obtained without the porous material.