DIY
The easiest way to make these, and how you can make them no-sew, is by using an old shirt sleeve. I went to the thrift store and found several awesome button-up shirts in fun colors for SUPER cheap to use just for this project.
Next, you will need to measure out your twine. You will want it to be about 6″ longer than your piece of material.
Turn your material inside out. Slide the knotted twine through the middle of the material, and stick the knot out the other side.