Voids and Air Traps

Voids and air traps are empty spaces or air pockets within the molded part caused by inadequate venting or trapped air during the injection process.


Voids and air traps are common defects encountered in injection molding, characterized by the presence of empty spaces, air pockets, or incomplete filling within the molded parts. These defects occur when air or gas becomes trapped during the injection molding process, resulting in compromised part quality and functionality. Voids and air traps not only affect the aesthetics but can also lead to structural weaknesses and dimensional inaccuracies. Understanding the causes of voids and air traps 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 voids and air traps, identifying their root causes, and providing insights into minimizing these injection molding defects.

Causes of Voids and Air Traps

Voids and air traps can occur due to several factors related to the injection molding process:

  1. Inadequate Venting: Insufficient venting in the mold cavity can lead to the entrapment of air or gases released during the injection process. Lack of proper venting prevents the escape of air, causing voids and air traps.
  2. Poor Gating Design: Improper gate design can cause air to become trapped during the filling process. Small or constricted gates restrict the flow of material, leading to air entrapment and the formation of voids.
  3. Material Degassing: Certain materials, such as polymers with high gas solubility or hygroscopic properties, release gases during the melting and injection stages. Inadequate degassing of the material before injection can result in trapped gases and subsequent void formation.
  4. High Injection Speed: Excessively high injection speeds can cause turbulence and air entrapment within the mold cavity. The rapid material flow can trap air pockets, leading to the formation of voids.
  5. Mold Design: Inadequate mold design, including poor cooling or improper runner and gate configurations, can contribute to the formation of voids and air traps. Inefficient cooling can result in localized shrinkage, creating voids within the part.


To minimize the occurrence of voids and air traps and achieve visually appealing and structurally sound molded parts, manufacturers can adopt the following preventive measures:

  1. Venting Optimization: Ensure proper venting in the mold to allow for the escape of air and gases. Incorporate venting channels or vents strategically in areas prone to air entrapment, facilitating the release of trapped air.
  2. Gate Design and Placement: Optimize gate design and placement to promote smooth material flow and minimize the risk of air entrapment. Utilize larger gates or multiple gates to improve filling and reduce the likelihood of void formation.
  3. Material Degassing: Prioritize material degassing by adequately drying or preheating hygroscopic materials and using appropriate processing techniques to eliminate trapped gases before injection.
  4. Injection Speed Control: Optimize injection speed to achieve controlled and uniform material flow. Avoid excessively high injection speeds that can lead to turbulent flow and air entrapment.
  5. Mold Design Considerations: Ensure proper mold design, including adequate cooling, to prevent localized shrinkage and the formation of voids. Optimize runner and gate configurations to facilitate smooth material flow and minimize air entrapment.


Voids and air traps pose challenges in injection molding, affecting the quality and functionality of molded parts. By understanding the causes of these defects and implementing preventive measures, manufacturers can effectively minimize their occurrence. Optimization of venting, gate design, and placement, material degassing, injection speed control, and mold design contribute to mitigating voids and air traps. By addressing these defects, manufacturers can produce visually appealing, structurally robust, and high-quality molded parts, ultimately improving customer