Picking fabric as bellows building material is not an easy job, for what bellows needs is the fabric as thin as possible, but can block the light away.
Darkroom cloth is thin enough, but if you think it can totally keep light away, think it twice.
Maybe it can block normal strength of light beam, but under the strong sun light, you should be cautious. I had mentioned this in previous post of preparing bellows material.
And I also mentioned that material for bellows that camera manufacturing companies picked, are rarely found in the market for common people, I believe that they are custom made exclusively for cameras.
So not only we pick darkroom cloth as inner layer for they are easy to get, and we need to apply one or two layers of acrylic paint on it to enhance the light blocking.
But how do we know this do provide absolute light blocking function??
Well, let's find out.
Overlay darkroom cloth which has been sprayed with acrylic paint, and the leatherette you pick as outer layer on a flash light, flash face up.
Turn on the power, and trigger the flash in a dim lit room, inspect with naked eyes, if any light coming out of the surface of the leatherette, it means acrylic spray is not thick enough.