Dominant viola strings have a synthetic nylon core which has all of the wonderful attributes of a gut core, but will last much longer and will not break down like gut strings. The C,G and D strings are all silver wrapped, while the A is aluminum. They are warm and very responsive and also well known for uniformity of sound across the range. Players also say they notice less 'timbre' difference when comparing same pitch on neighboring string. These 141 strings are medium tenision.