From D'Addario:

XL Chromes are among the warmest, mellowest bass strings we have to offer. These flat wound strings provide an ultra-smooth feel and a dark, yet warm tone, while allowing movement across the fretboard with no finger noise. Made with a high carbon steel core, Chromes stainless steel flattened ribbon wrap wire is expertly wound onto a series of interlocking under-windings, then precisely polished for unparalleled smoothness and a tonal presence which blends beautifully into the mix. This 45-100 Regular Light gauge set has a nice even tension, bright tone, and tight low-end.