The core is synthetic fibers, insensitive to humidity and temperature changes.   There is a break-in period as these strings stretch before becoming stable.  Some customers report it can take 10 days or so.  Brand is identifiable by orange thread with black spiral at the tailpiece end.  Pirastro recommends substituting a Passione steel core A to give the entire set a warmer sound.


$39.13   A    chrome winding, steel core                  Black at peg end

$42.58   D    chrome winding, synthetic core           Orange at peg end

$65.00   G    tungsten winding, synthetic core         Brown at peg end

$96.00   C    tungsten winding, synthetic core         Violet at peg end