From D'Addario:

XS Nickel coated electric guitar strings provide the longest life of any D’Addario electric guitar string. Coated with our groundbreaking XS coating, these premium electric strings attain maximum life and a smooth, fast feel without dampening their outstanding tone. Constructed with a NY Steel core, reformulated nickel-plated steel wrap wire, and Fusion Twist technology, XS Nickel strings boast superior strength and tuning stability, plus richer harmonics, greater clarity, and remarkable definition with every sweep, slide, and bend. 9.5-44 Super Light Plus strings are a good middle ground between 9s and 10s, and are good for balancing tension between varying scale length guitars.