Spectrex IV transmits strikes better than any other line because of its near-zero stretch factor.

Spectrex IV Spectrex IV is a four carrier Spectra® braid. Each carrier has up to 60 strands of Honeywell's highest quality Spectra and is braided into a single line totaling up to 240 strands. The line is cross-linked with a color matrix locking the color into the fibers to ensure color stability. We then apply a reinforced resin system to increase tensile strength and make the line hydrophobic.

So what does this mean to the angler who is not an engineer? It means increased sensitivity because of near-zero stretch factor. It means increased line capacity because of the high strength in comparison to the diameter, and it means a line that has an unlimited life on the reel because the line is UV resistant and hydrophobic.