Traditionally, tea bags have been square or rectangular in shape. More recently circular and tetrahedral bags have come on the market and are often claimed by their manufacturers to improve the quality of the brew. Environmentalists prefer silk to nylon because of health and biodegradability issues. Another material for tea bags is Soilon (PLA mesh), made from corn starch. Empty tea bags are also available for consumers to fill with tea leaves themselves. These are typically open-ended pouches with long flaps. The pouch is filled with an appropriate quantity of leaf tea and the flap is closed into the pouch to retain the tea. Such tea bags combine the ease of use of a commercially produced tea bag with the wider tea choice and better quality control of loose leaf tea.