Pro-Arte synthetic core cello strings have a warm mellow tone are less sensitive to humidity and temperature changes and break in quickly. Pro-Arte strings are manufactured at a lower tension in order to maximize bow response tonal blend and playability. Pro-Arte is a perfect choice for players seeking a warm dark tone. Scaled to fit 4/4 size down to ¼ size these medium tension strings are optimized to the needs of a majority of players. All D Addario strings are designed engineered and manufactured in the USA to the most stringent quality controls in the industry.