Provided is a die plate assembly for an underwater pelletizing system, wherein molten plastic flows through a die plate and exits into a fluid bath for further processing. The assembly provides a seal against water leakage and effective insulation to prevent heat loss from a heated die plate. The assembly includes a die plate having a plurality of through holes for receiving fasteners for mounting the plate to another portion of the pelletizer system, and at least one insulation chamber for insulating the die plate from the fluid bath located on a downstream side of the die plate. The assembly further includes at least one gasket covering one or more of the through holes to seal one or more through holes from the fluid bath.