Smoother than ever, tougher than before. If Berkley FireLine Crystal Fishing Line were any clearer, it would be a monofilament. This is the next generation of FireLine and its smooth right out of the box, so you can expect the easy handling and fast casting youve come to depend on. Thermally fused and incredibly thin, this fishing line remains the go-to translucent superline for near invisibility. Its the ultimate in diameter-to-lb.-test ratios and it delivers the stealth needed for spooky fish and clear water. Cancer and Reproductive Harm- www.P65Warnings.ca.gov. Type: Line.