Pad printing is a process in which a silicone pad is used to transfer ink onto the surface of a part. It is a very efficient way of printing onto curved surfaces or otherwise complex geometry.
Eco-Pro: Uses very little ink. Energy efficient process.
Eco-Con: Can wear off eventually, making products look old (and therefore more likely to be thrown away or replaced).
Question the premise of the finish:
Is a different color necessary for the logo/graphic I want to print? Can I get a nicer effect by engraving or adding a detail in the injection molding tool so that I don't use ink at all?
Same finish, better process: Pad printing on the back of clear parts can give the same effect while making the part less susceptible to wear.
Materials: Almost any material.
NOTES: Pad printing is most often used for detail finishing (logos, letters on keyboards, etc.) so it is not accurate to compare the footprint of pad printing to full part finishes like painting. However, the ID requirements of a product often require more than just raw material finishes, so pad printing on an unpainted part can be thought of as a good alternative to painting in order to achieve the same effect.