A 2011 study by the United Kingdom's Environment Agency evaluated 9 categories of environmental impacts caused by grocery bags and found that reusable plastic bags cause significantly less harm in all 9 categories than the others. The study also found that disposable plastic bags cause less harm in all 9 categories than reusable cotton bags and disposable paper bags. The environmental impacts of supermarket bags are dominated by the energy and raw materials needed to manufacture them. Plastic bags are inexpensive because they require relatively small amounts of energy and raw materials to produce. These same attributes that make plastic bags affordable and light also make them easier on the environment than alternatives like paper bags and reusable cotton totes.