Yellow jam string. Part polyester part cotton.

From Julius
"I like useing this on all my slack string yoyos. It's softer and tougher, so if you have  an audience sitting in front of you, this string will provide added peace of mind." I charge $0.50 if you buy a single one of these off me. If you buy 100, you're saving $35.00. Not only a good idea, but a great idea."