I have had a lot of really positive feedback on my recent text titled Bellows Building. I would like to thank everyone for the kind comments. There have been several inquiries for more information regarding Railroad Board, exactly what it is and where to purchase.
Railroad Board is the best material for bellows ribs. It is a smooth, thin, Bristol-type board, colored on both sides, that is used for signs, posters, mailing cards, tickets, tags, and so forth. Thicknesses are 4 ply (about .017″ or .43 mm) and 6 ply (about .022″ or .56 mm) and is available in 22″ × 28″ sheets. I recommend 4 ply for small bellows smaller than 8×10 and 6 ply for larger bellows.
You can purchase Railroad Board by the sheet or in bulk packages from Dick Blick. I would recommend black material and here are the stock numbers and the direct link to their on line CATALOG ;