You are only limited by your imagination and willingness to experiment with the plants you come across in nature. Both of these members of the milkweed family produce a light brown, almost indestructible cordage. The plants can be easily identified by their red stalks. You can use them for a wide variety of projects ranging from bow strings to fishing lines and snares. The fiber works exceptionally well for fletching arrows.
Most sources say to gather the plants when dry, then pound and clean the fibers.
Another way is to gather them green and peel down from either side of the base of the plant. You will be amazed at how much more useable cordage you will get this way. Be sure to carefully dry the fibers before using. You can also pick large quantities of the plants while green, remove the leaves, dry and store for later use. This will give you stronger fibers than if picked later on into winter.