Jetting is a defect characterized by erratic material flow, resulting in a visible “jet” or streak on the surface of the molded part.


Jetting is a common defect encountered in injection molding, characterized by the formation of irregular, streak-like patterns on the surface of molded parts. This defect occurs when the molten material is expelled forcefully into the mold cavity, causing turbulence and poor material flow. Jetting not only affects the aesthetics but can also lead to dimensional inaccuracies and compromised part performance. Understanding the causes of jetting and implementing effective preventive measures are crucial for manufacturers striving to produce high-quality molded parts. In this article, we delve into the intricacies of jetting, identifying its root causes, and providing insights into minimizing this injection molding defect.

Causes of Jetting

Jetting occurs due to several factors related to the injection molding process:

  1. Injection Speed: Excessively high injection speeds can cause the molten material to shoot into the mold cavity with excessive force, resulting in turbulent flow and jetting. Rapid material flow can also push air or gases ahead, leading to trapped air pockets and surface defects.
  2. Thin-Walled Sections: Molded parts with thin-walled sections or long flow paths are more prone to jetting. Insufficient material flow in these areas can cause jetting as the material is unable to fill the cavity uniformly.
  3. Gate Design and Placement: Improper gate design or placement can contribute to jetting. Small or restricted gates can lead to high shear rates, increasing the likelihood of turbulent flow and jetting.
  4. Material Viscosity: Materials with high viscosity are more susceptible to jetting due to their reduced flowability. High-viscosity materials require careful consideration of processing parameters to achieve optimal flow and minimize jetting.
  5. Mold Temperature: Improper mold temperature control can affect material flow behavior and contribute to jetting. Inadequate cooling can lead to premature solidification and hinder material flow, resulting in jetting defects.


To minimize the occurrence of jetting and produce visually appealing molded parts, manufacturers can adopt the following preventive measures:

  1. Injection Speed Optimization: Control and optimize the injection speed based on the material properties and part design. Slower injection speeds allow for smoother material flow and reduce the chances of turbulent flow and jetting.
  2. Gate Design and Placement: Ensure appropriate gate design and placement to promote balanced material flow and minimize jetting. Consider using wider gates or multiple gates strategically positioned to encourage smoother flow into the mold cavity.
  3. Mold and Part Design Considerations: Optimize the mold and part design to minimize thin-walled sections and long flow paths. Well-designed mold and part geometry facilitate uniform material flow and help reduce the occurrence of jetting.
  4. Material Selection and Processing Parameters: Select materials with suitable flow properties for the specific part design and application. Adjust processing parameters such as melt temperature and injection pressure to optimize material flow and minimize jetting defects.
  5. Mold Temperature Control: Proper mold temperature control is critical in minimizing jetting. Maintain the recommended mold temperature range to ensure uniform material flow and prevent premature solidification.


Jetting is a common challenge in injection molding, impacting the quality and appearance of molded parts. By understanding the causes of jetting and implementing preventive measures, manufacturers can effectively minimize its occurrence. Optimization of injection speed, gate design, mold and part geometry, material selection, processing parameters, and mold temperature control are essential in mitigating jetting defects. By addressing this defect, manufacturers can produce visually appealing, dimensionally accurate, and high-quality molded parts, ultimately improving customer satisfaction, reducing waste, and optimizing overall efficiency in the injection molding process.