The “green bags” are designed for fruits and vegetables that ripen by the production of the plant hormone, ethylene. Ethylene gas is produced in copious quantities by certain fruits, most notably bananas. As the concentration of ethylene gas increases in an enclosed environment, the fruit ripens faster. Removal of ethylene helps keep fruits from over-ripening quickly. The green bags are made of a polymer that allows the escape of the gas while keeping others, and some of them actually use additives to the film to absorb other gases that promote ripening or deterioration.
The green bags do work for certain types of produce. Some caveats–the shelf life is extended as long as the product is very dry (mold growth appears to be a problem in damp produce). Also, the bags have a shelf life and can only be reused 10 times. If you intend to eat a product quickly, say strawberries, it might not make economic sense to use the green bag when normal plastic film would work.
-contributed by Sam Beattie, ISU Food Safety Extension Specialist