This blue material meets the requirements for the blue color inside the traps down the right and left side of the New Generation Stormtrooper helmet. This particular Stormtrooper is the one seen in Rogue One, The Mandalorian, Kenobi, and Andor.
It is cotton and breathable. You can see your finger through it, but just barely.
The color most are going for is painters tape blue. This is absolutely the closest material I have found to that color.
You’ll get enough for a left and right side.