Pistons and clutch assemblies including the pistons are disclosed. A clutch assembly may include at least one rotatable clutch plate, a reaction plate arranged to rotate with and apply a force to the at least one rotatable clutch plate, and a spring configured to urge the reaction plate away from the at least one rotatable clutch plate. A piston may be provided including a first segment formed as a plate and defining an internal space between the first segment and a housing and a second bulk segment that occupies at least a portion (e.g., 50% by volume) of the internal space. At least one bearing rolling element may be arranged between the reaction plate and the piston to permit relative rotational motion therebetween. The second bulk segment may be formed of plastic or a plastic composite and may reduce the amount of hydraulic fluid present in the internal space.