A resin panel of which contact surfaces of a rear wall to be in contact with another member are made unlikely to deform while reducing the weight of the resin panel. The panel includes a rear wall having a plurality of contact surfaces to be in contact with another member, and a front wall opposing the rear wall with an interval therebetween, the resin panel including a plurality of ribs obtained by indenting parts of the rear wall toward the front wall and welding the parts to an inner surface of the front wall, wherein a wall thickness of the front wall is generally equal to or smaller than a wall thickness of the rear wall.

An extrusion blow molding method includes detecting an exit velocity of a tube exiting a head during a blow molding cycle for forming the tube. A melt accumulator receives part of the melt conveyed by an extruder or discharges melt in addition to the melt conveyed by the extruder in dependence on the detected exit velocity. The melt accumulator discharges melt if the detected exit velocity is less than a target value for the exit velocity and receives melt if the detected exit velocity is greater than the target value for the exit velocity.

A resin panel of which contact surfaces of a rear wall to be in contact with another member are made unlikely to deform while reducing the weight of the resin panel. The panel includes a rear wall having a plurality of contact surfaces to be in contact with another member, and a front wall opposing the rear wall with an interval therebetween, the resin panel including a plurality of ribs obtained by indenting parts of the rear wall toward the front wall and welding the parts to an inner surface of the front wall, wherein a wall thickness of the front wall is generally equal to or smaller than a wall thickness of the rear wall.

A resin panel of which contact surfaces of a rear wall to be in contact with another member are made unlikely to deform while reducing the weight of the resin panel. The panel includes a rear wall having a plurality of contact surfaces to be in contact with another member, and a front wall opposing the rear wall with an interval therebetween, the resin panel including a plurality of ribs obtained by indenting parts of the rear wall toward the front wall and welding the parts to an inner surface of the front wall, wherein a wall thickness of the front wall is generally equal to or smaller than a wall thickness of the rear wall.