Payment for the deal, which values the Extrusion business at €16.2mln (£14.4mln) when free of cash and debt, will be made in cash.
Directors of FTSE 250-listed Essentra said they intend to use the proceeds to strengthen the balance sheet.
In the past calendar year, Extrusion, which focused on plastic extrusion where hot plastic is formed into items such as tyres, pipes, sheeting and window frames, contributed operating profit of £1.2mln to the group.
Chief executive Paul Forman said: “The sale of Extrusion not only represents good value for Essentra's shareholders, but also provides the business with a strong platform for future successful growth given Inter Primo's established presence in the extrusion industry."
Essentra also divested the PPT business from the Specialist Components division for £38mln in January.
Shares in the group, up more than 14% since the start of the year, were flat at 404.8p on Tuesday.