Paper or plastic, you ask?
Many plastics, like commercial shopping bags, contain chemicals often referred to as "slip agents," which are derived from the stearic acid in animal fat. They essentially prevent the polymers from sticking to metals during manufacturing and clinging to each other afterward.
Apparently, manufacturers of biotechnology are concerned lately about beef fats used in plastic materials that come in contact with bioprocess fluids. Why? Because of prions. (Aka “mad cow disease.”)
Here is an interesting link regarding the use of animal byproducts in plastic materials:
Regarding paper bags - guess what? Our cats might be attracted to the glue! Yes, many glues are animal/fish based and out kitties can smell it a mile away!
Here is another intersting link that will keep you up at night!
And, yet another, that gives the breakdown on paper coatings and bipolymers used in the manufacturing of paper. This is a pretty lengthy article, so you might want to use the listings on the left side of the page and go down to "Biopolymers and Biocomposites for Paper Coatings" and red through it.
The things they just don't tell us!