P-Line C21 Copymer Filler Spool Used by both professional and amateur anglers Superior strength, and stability Made using the highest quality components A copolymer line made with two types on nylon, C21 synergistically creates the ultimate line for spinning or bait casting reels, without putting a big dent in your wallet! Castability is the most important attribute for an angler, and C21 delivers with a soft construction which literally flies off the reel with virtually no memory.