Underworks 983 (Tritop) binder.
So, what's it made from?
The Underworks 983 is 70% nylon and 30% spandex. The front half of the binder is three layers while the back side is one layer. It's impeccably well-sewn together and generally lasts for up to 6-8 months of daily wearing before the material starts to tear.
What sizes does it come in?
This binder is available in a wide range of sizes. Here's the list:
Source: (Tyler a.k.a. copper-rose)