3M type#850 black tape; very black, very thin, very sticky, no bleed , no creep adhesive, rather expensive. The entire bellows of my Omega D2V is covered in this stuff and the result looks like and behaves like new.
This "ultimate bellows repair tape" also works well on cameras. My Tachihara 8x10 is wearing some of it now. Because the tape is so strong, thin, and flexible complete bellows should be made out of it in the first place. I wish it didn't cost me $100 a roll.