BodyFlex Tube

It's used on the head, to create a lightweight body, to segment up the body of big streamers and hold open materials, creating volume while being lightweight, making it easy to cast all day.

Here is a video showing what the "BodyFlex Tube" is used for:

Here is a video showing the tying procedures:

Here is a video that shows photos of several streamers, including close-ups of the use of the "BodyFlex Tube"