Traditionally, hemp, also known as industrial hemp, was a thread or cord made from the fibers of the Cannabis sativa plant. Since hemp fibers are good at absorbing moisture, they usually would be coated in beeswax or cobblers wax, a mixture of beeswax and resin.
Modern hemp is usually made out of cotton or linen fibers. It generally comes in three spool forms for Highland bagpipers: plain yellow, waxed yellow, and waxed black. Plain yellow and waxed yellow hemp are made of cotton fibers spun into a thin string. Waxed black hemp is made of linen fibers, slightly thicker than the cotton. Both waxed varieties of hemp are coated in paraffin wax.
The two types of yellow hemp are good at absorbing moisture and tend to swell when exposed to it. Black hemp does not absorb as much moisture and the heavy paraffin coating creates a harder, slightly sticky surface.