I helped desig a pneumatically powered soft finger for a soft robotics course group project. The finger is made out of an Ecoflex 30A Silicone elastomer that we molded in a two part molding process.
The first mold creates the internal air cavities of the finger with an overmolded piece to connect to the air supply. The second mold is a rectangular tray (not pictured) that is filled with silicone and a thin fabric to create the bottom of the finger. Once both molds have cured, the two pieces are glued together with silicone.
When the finger is inflated with air, the bottom of the finger does not expand due to the thickness of it and the added stiffness of the fabric. Instead the top side of the finger expands which causes the finger to curl.