Update: I took at closer look my previous mask and have officially decided I am in the process of creating another. This time however, it is my very intent to capture EVERY authentic detail about Cillian Murphy's mask used in the film.
That being said, I'm looking through every photo of his mask that I can possibly find: finding what color of burlap that is used, analyzing what components make it dirty and spotted in parts of the mask, where exactly the rips and stitch patterns are, every wrinkle/pleat I would need to make either by sewing or ironing, EVERYTHING.
And for references undergoing what I'm attempting, here's a few photos of what we have to work with; some details I find fascinating.
Here's where it get's interesting; it would seem that there leather buckles and straps that been installed inside of that mask. One could argue that it might be adjustable, but the fact obviously is that the mask is tailored to Cillian Murphy's head size, as well as the burlap being created AROUND his breathing apparatus; I'm theorizing that the straps indeed belong to whatever respirator mask he's got going on inside.
And another thing: it also seems my noose theory is something along the lines of what the creators had in mind. It would seem the noose is a made fit, and it connects higher above on the back of the head. That way there was no adjusting of the noose: that the mask is all in the end one piece, and in be thrown on and off without any tightening or loosening. And how the noose is shaped: on the left it goes up over the mask and to the back, while on the right about 2-3 inches a way, a hole was made to slide the rope in and to the back as well. Small details like this what gives the mask it's shape, and as grungy and as thrown-together as it is, it's actually brilliant in it's design and little tailoring cheats. This also provides an extra safety precaution of not strangling yourself, which is a plus!