The new part isn’t much different from the OT pilot flare belt. The flares are shaped differently, but it’s still a strap of webbing that wraps around the leg. It is thinner at only one width of 2″ seatbelt webbing. It’s darker than the gray nylon used at the knee of the suit, so it’s most likely either a charcoal or weathered black. The interesting thing is that unlike most American seat belt webbing, there aren’t visible panels (the woven stripe patterns). The panel-less webbing appears to be more common in the UK.
There are seam lines visible on some of the flares, so they were most likely molded. A 3D printer pattern is available here and finished flares can be ordered here. The coloring looks like weathered steel, so I used Rust-Oleum in Aged Metallic Weathered Steel to paint mine and it’s a great match.
Poe wears his across the bottom of the top set of leg pockets on his left leg. Other pilots in the film are shown wearing them on either leg and at different heights, including higher up on the thigh. For shorter pilots, the thigh position is almost mandatory.