Processed Chlorine Free is not to be confused with Elemental Chlorine Free (ECF) which means no chlorine was used, but chlorine derivatives are permissible. Elemental chlorine bleaching was phased out in the United States in April 2001 per the EPS's Cluster Rule. Elemental chlorine free remains preferable to any process that still uses pure chlorine. Enhanced elemental chlorine free further reduces energy and chemical use. Most environmental groups consider Processed Chlorine Free to be the most preferable.