The chemical reactions and pathways involving hyaluronan, the naturally occurring anionic form of hyaluronic acid. Hyaluronan is a type of non-sulfated glycosaminoglycan composed of the repeating disaccharide unit beta(1,4)-D-glucuronic acid-beta(1,3)-N-acetyl-D-glucosamine. [ http://www.ncbi.nlm.nih.gov/pubmed/35536932 http://www.ncbi.nlm.nih.gov/pubmed/33171800 ]