Golf club heads and methods to manufacture golf club heads

A golf club head comprising:

• a body portion having a toe portion, a heel portion, a top portion, a sole portion, a rear portion, a front portion having a face portion with a face portion thickness extending between a front surface and a back surface, and an interior cavity;
• an elastic polymer material in the interior cavity, the elastic polymer material being associated with an elastic polymer material volume;
• and
• a radiocontrast material included in the elastic polymer material,
• wherein the face portion thickness is related to the elastic polymer material volume by the equation 0.01≦Tf/Ve≦0.2, where Tf is the face portion thickness in units of inches, and Ve is the elastic polymer material volume in units of in3.

A golf club head comprising:

• a body portion having a toe portion, a heel portion, a top portion, a sole portion, a rear portion, a front portion having a face portion with a face portion thickness extending between a front surface and a back surface, and an interior cavity;
• and
• an elastic polymer material in the interior cavity, the elastic polymer material including a radiocontrast material,
• wherein an elastic polymer material volume associated with the elastic polymer material, a body portion volume associated with the body portion, and the face portion thickness are related by the equation Ve=a*Vb+b+c*Tf, where Ve is the elastic polymer material volume in units of in3, Vb is the body portion volume in units of in3, Tf is the face portion thickness in units of inches, a≅0.48, b≅−0.38, and 0≦c≦10.