How to Mold With HDPE Regrind

By Amy Rodriguez

Updated September 26, 2017

Plastic is used to make a variety of items, from drink containers to heavy duty piping. Plastic manufacturers have also found ways to recycle old plastic, such as high density polyethylene (HDPE). Used HDPE containers can be broken down into pellet sizes. These pellets, or regrind, are typically melted down through blow molding machines, creating new HDPE containers. However, HDPE regrind must be molded in a specific manner for the best results.

Verify that the HDPE regrind pellets are clean. Do not leave regrind stock in open boxes or containers. Any contaminants entering the bulk regrind compromises the final HDPE plastic quality.

Power on the blow molding machine. Allow the machine to warm up to its specified heat temperature. The temperature varies, based on the machine's manufacturer, regrind percentage and final product type.

Fill the blow molding machine's hopper with a mixture of new HDPE and regrind HDPE pellets. Commonly, 35 percent of the entire pellet supply in the hopper is HDPE regrind. However, the percentage can increase to a maximum of 70 percent, depending on the intended product and regrind quality.

Allow the machine to pull regrind pellets into its assembly for melting processes. Ensure that the pellets are not stuck within the hopper, hindering the melting process.

Inspect the product molded from the machine. Verify that it does not have anomalies, such as holes or scorch marks, along its surface.

Items you will need

  • Blow molding machine

  • HDPE regrind pellets

  • HDPE virgin pellets


Molding with regrind does not require excessively hot temperatures. Consult with the product manufacturer to identify the coolest temperature allowable. Use the coolest molding temperature so that the final product does not need to cool for as long, which minimizes the potential for damage.


Do not mold HDPE regrind with 100 percent regrind pellets. This percentage lowers the product's quality and structure. In addition, only trained personnel should operate a blow molding machine. Injury can occur from the machine's hot temperatures if you accidentally touch the surface.