An advantage of compression moulding rubber keypads is that it is possible to integrate a range of colours. Just like colourful recycled plastics, the coloured parts can be moulded in the same sequence, in which case the joint line is irregular.
Rubber compression moulding is used to produce parts with various levels of flexibility. Live hinges and tear lines can be integrated into the design to eliminate secondary operations. Another major advantage of working with rubber is that draft angles can be eliminated so buttons can have vertical sides (no taper).
Image from The Manufacturing Guides