Pirastro Tonica Viola C: 

Tonica strings have a core made from nylon. They produce a lively well-rounded sound, perfectly balanced across all four strings. Responding instantly to any bowing style, they reward both player and listener with an open and direct sound. With substantially reduced background 'hiss', players can sustain a more even tone helping to achieve smoother string crossings. With a highly responsive left-hand feel, Tonica strings remain very easy to play all the way up to the highest positions.