Zyex by D'Addario Zyex Composite Synthetic Core Viola Strings produce an extremely warm, rich sound. Zyex uses a new generation of synthetic material, creating strings that are extremely stable under drastic climatic conditions. Zyex strings settle in on the instrument very fast, within a matter of hours. Zyex has a warmer sound than most other synthetic core strings and they have excellent projection making them exceptional for soloistic use as well as symphonic. All strings are composite synthetic core with the windings listed below.