Aquila Bionylon is the first eco-friendly synthetic string in the world. These Ukulele strings are made of rounded, smooth Bionylon monofilaments - a new material discovered by Aquila - that also boasts excellent acoustic and mechanical properties. Bionylon is 100% a plant's derivate (castor oil): this allows a reduction of more of 50% of carbon dioxide's emissions in the atmosphere during the polymer-synthesis than the other common Nylons employed for musical strings. Warm and mellow perfomances!