Star filler
A star filler (also known as cross filler, splines, separators and crossweb fillers) is a type of plastic insert in Cat 5 and Cat 6 cable which separates the individual stranded pair sets from each other while inside of the cable. It increases the thickness and density of the cable but reduces crosstalk and is commonly used only in higher-performance Cat 6A cable, but is also sometimes seen in Cat 5e.