I have a Dalite Model C 1.78:1 pulldown screen that I'd like to make removable black border strips for to use when watching 2.35:1 movies. I've read on this forum about using magnets as a way of temporarily attaching the fabric which sounds great but my question is about what kind of material to use that won't sag in the middle since it's only feasible for me to put magnets at each side of the screen.
My specific screen is 9' wide and the black strips would need to be 6" tall. 9' is quite wide for material to not sag, with it only being attached at the sides. I'm wondering if others here have experimented with material and can say what materials sagged and which didn't. There is a side issue of trying to get a similar black level to the rest of the black border of the screen so the removable border blends well with the shade of black of the black border of the screen.
Any input would be greatly appreciated. Thanks in advance!