RIO makes both a clear and pink shock gum material. The pink material is stronger than the clear and makes am excellent strike indicator.
I make my own shock gum sections by cutting a piece approx. 12 " in length. Tie a perfection loop in both ends. Ideally, you want the loop to keep the loop small so it will pass easily through your guides, if need be. After I tie both ends, I hold the loop of the knot with one hand and stretch the loop with the other. This pulls the knot down tightly and minimizes the size. As the loop is tightened, I add a drop of superglue to secure the knot. I have found from past experience this keeps the knot from coming undone.