The U.K. Environment Agency has come up with the answer; a low-density polyethylene bag, when used four or more times, has a lower carbon footprint than single-use bags of any type, whether high-density polyethylene, paper or cotton. A recently released report, “Life Cycle Assessment of Supermarket Carrier Bags,” showed that the key to reducing a bag’s environmental impact is multiple use. Premium, heavier weight bags made of woven plastic, for example, have a lower carbon footprint than single-use bags after being re-used only 11 times. “A significant part of the environmental impact … is associated with the resources used in their production. All multi-use bags need to be re-used as much as possible to reduce their relative environmental impact and be responsibly recycled at the end of their life,” according to the report.