Increasing attention is being paid to the environmental consequences of the plastic 'single-use' shopping bags provided to customers by supermarkets and other retailers. Not only does the production of these bags represent a wasteful use of natural resources, but there are also problems surrounding their disposal. For instance, the bags often end up as litter, and in the marine environment, they kill many animals that become entangled in them or mistake them for food. Numerous countries and individual cities have banned these bags, but experts on the environmental impacts of products warn that no perfect alternative exists. Whether using fabric or heavier plastic, manufacturing bags that are stronger and thus more reusable requires significantly greater quantities of natural resources than the vilified 'single-use' ones.