Jetting (jet flow) is an external view defect in which a wavy pattern appears on the surface of the molded product. Jetting occurs because the plastic injected into the cavity from the gate suddenly flows into the cavity at a very high speed, and after colliding with the wall on the side opposite to the gate, proceeds to fill the cavity from the area surrounding the gate. Although the physical phenomenon is different from the injection molding formation of thermoplastic material, it is similar to the unstable and wavy ejection of toothpaste into the air when a tube of toothpaste is suddenly squeezed strongly. This can be thought of as the behavior of a viscous fluid.

The following methods can be considered as the countermeasures against jetting.

Mold related countermeasures

	1.	Widen the gate. Make sure that the gate is not too thin compared to the wall thickness of the molded product.
	2.	Change the position of the gate, and move it to a location where successive filling can be done from near the gate.
	3.	Provide a core in the vicinity of the gate so as to obstruct the molten plastic that tries to suddenly fill the cavity.

Molding condition related countermeasures

	1.	Make the injection speed lower so that the filling is successively done from the vicinity of the gate.
	2.	As a corrective measure, set the cavity surface temperature a little higher so that the wavy patterns disappear. However, with this method, understand that the condition of the flow control is still unstable