The answer is neither. Both are environmentally harmful, and the question of which is more damaging has no clear-cut answer. On one hand, plastic bags degrade slowly in landfills and can harm wildlife if swallowed; in addition, producing them uses vast amounts of water and pollutes the environment. On the other hand, producing the brown paper bags used in most supermarkets uses trees and also pollutes the air and water. Overall, white or clear polyethylene bags require less energy for manufacture and cause less damage to the environment than do paper bags not made from recycled paper. Instead of having to choose between paper and plastic bags, you can bring your own reusable canvas or string containers to the store, or you can save and reuse any paper or plastic bags you receive (if the store allows it—some places have health codes that do not allow you to reuse paper or plastic bags).