Customers who order polyethylene plastic film at one thickness in writing then tell us verbally to run a different gauge, usually thinner, are either cheating their customers on weights and measures or making sure they get proper yield with no cost overrun from overgauged film.
Or they advise us to run nothing thinner than the thickness specified.
Either one puts us in a tough spot from what is referred to as "yield" standpoint defined as the area derived from plastic film invoiced by the pound.
Either scenario can lead to a complaint or claim usually justified by one sample which is not even out of the industry standard plus or minus 10 %.
Here's what happens in real life: The operator sets up the order. When the conditions of width, resin recipe and polyethylene film thickness ( a tad on the thick side ) are right, the first roll(s) of custom saleable film is started. The target weight of the first roll of layflat tubing or first two rolls in the case of single wound sheeting will be "heavy" or over the target weight. Adjustments to the process conditions are then made. By the third roll of layflat tubing or "set" of sheeting, the roll weights will be lighter than the target weight. Over the course of the run, the customer will get more area than what is referred to as the " theoretical" yield. Theoretical yield is calculated by dividing the yield, or weight per 1,000 lineal feet, into the total pounds shipped. Example: 35" X 4 mil sheeting weighs 56 pounds per 1,000 lineal feet ( the "yield" = 56 pounds ). If 3,158 pounds are shipped, the theoretical yield, or number of feet the customer should have gotten out of 3,158 pounds is 56,392.
On short runs, there simply is not enough time to fine tune for yield.
We are not set up to run one ostensible gauge and ship a different plastic film thickness. Everything from our acknowledgements to packing lists contain the same exact information which goes to our shop floor.