Aluminum is also used for a soft feel and lightweight. Graphite, polymers and other plastics are used to make a putter head that is very resilient and very light. These materials generally make the head more expensive. Inserts Putter heads have been the focus of a lot of experimentation in materials. Some have lightweight composite inserts in the face, which, by ratio, places more weight in the toe and heel.
Inserts are a relatively new design element in putters.
They're intended to provide greater response at contact. Some companies have experimented with rubber faces, aluminum honeycomb-like structures, and the like. The insert conforms to the ball on contact and generates a softer feel through the shaft and to your hands. The result is a more controlled roll. Weight Weight is the greatest contributor to how the putter feels in your hands.