Low hardness, resilient golf putter insert

A golf club having a toe and an opposite heel, a sole portion and an opposite top portion, a forwardly facing exposed strike face, an opposite rearwardly facing exposed back face portion, a hosel, and a shaft, comprising:

• a recess defined in the strike face, said recess having at least a bottom surface spaced from the back face portion and a side wall surface extending between the bottom surface and the strike face;
• and
• an insert located in the recess formed of a first vibration dampening material comprising an insert material formed from the conversion reaction of a resilient polymer having sufficient amounts of polybutadiene, a free radical source, and a cis-to-trans catalyst, which reaction occurs at a sufficient temperature to form a polybutadiene reaction product which comprises an amount of trans-polybutadiene isomer greater than the amount of trans-polybutadiene isomer present before the conversion reaction.