This must be the most profitable item sold in shops.
I suddenly realized that this is what I was paying when I bought a piece of fish in a local supermarket and a very thin sheet of plastic was put on the scales the fish placed on top of it weighed then priced.
When I pointed this out to the shop assistant he said that "it didn't weigh anything"! I suspect this item that weighs "nothing" is purchased by the ton.
There was a study done on this, a few years ago, I can't remember the figures but it was something along lines that as there were several sheets to the gram. It was unlikely to seriously affect the cost of the product.
This does not just apply to the bit of plastic for fish , as xmas is coming up you will see oversized joints of meat for the annual family blow out. Some joints such as pork have huge wads of fat on them , they say its to aid cooking but , you pay the same price per kilo for the unwanted fat as you do for the joint of meat that you eat.