The front part is supposed to be 3D printed with flexible resin. Bare conductive ink is applied on the 3d printed "pill" that will be touching the PCB. A flexible PCB would allow a bendable, rollable keyboard.
A DIY flexible keyboard project; instead of using silicone, a SLA highly flexible resin is used.
I need an xvkbd layout for my smart phone I make them out of super glue and plastic bags now and it's very messy.