Cups, cartons and food wrappers made of paper might seem like they would be biodegradable, but many contain a plastic coating that can't be composted. Although plastic-free, sustainable paper products are available, they often let grease and oil pass through, weakening the paper and creating a mess. Today, scientists report they have developed a degradable polymer coating that can block this seepage and could lead to new biodegradable, paper-based materials.