Golf Club Components: Clubhead Cavity Back/Pad/Insert
Depending on whether the iron is designed as a blade or a cavity back, the portion of the clubhead directly behind the face will contain a hollowed out area — possibly filled in with a cavity badge or vibration-dampening polymer — or solid metal, often referred to as an insert today. That’s the pad essentially. The hollowed out area is a cavity back, which are known for being much more forgiving, and low-handicap players say less precise, than a blade or muscleback iron clubhead. Inserts and cavity backs are supposed to be especially helpful in lessening the damage done by a miss-hit.
Here’s a great example of a vibration-dampening insert. Sometimes irons are hollowed out as well.