The Inner Layer
I pick darkroom cloth as inner layer for it is easy to find, almost every store sells cloth has it, and it is cheap, but most of all, it is very thin, made in nylon so it is very sturdy and it won't stretch, this is important when you pick fabric material for bellows.
There are darkroom cloths with both side in black or one side in sliver, I won't choose silver version unless I planned to cover the bellows in lighter color as outer layer, such as red or white.
Although darkroom cloth are so called, but it is not 100 percent light proof, image below shows two pieces of darkroom cloth, left one has been sprayed with two layers of black acrylic paint,comparing with right one which in original condition.
Applying dull black acrylic paint can improve darkroom cloth in two considerations, make the surface much more dull matt, and to enhance the light blocking ability.
1. Squeeze some acrylic paint into a shallow dish, dilute with water in ratio about 3:1, with a wide flat brush brushes paint onto darkroom cloth surface, apply as little paint as possible each time, and make sure paint spray evenly, put it still for drying up, you can apply second layer of paint if feel necessary.
I applied one layer of acrylic paint to each side, to see which side gets the best dull surface, you can tell that one side is duller than the other.
After applying acrylic paint, cloth gets different touch, from nylon cloth into some kind of leather, and it surely improve the light blocking ability.
2. Inspect painted darkroom cloth, decide which side has duller mate surface, place duller side facing down. Lay the bellows layout template on top of the cloth, and trace the outline lines. With shape A and B template, draw top and bottom guide lines within each shape.
Now try place 4 rib pairs stripe shapes on it, remember always align with the bottom line.
And be reminded again each rib pairs strip shape has two more ribs beneath the bottom line, you should align third rib to the bottom line.
3. Fold each rib pair stripe shape between 2nd. and 3rd. rib at the bottom, forming a distinct folding line shows where the bottom line is when place the glued rib pairs. Or you can draw a line that place if you want it more clearer to see.