A company spokesman said 20 people were employed at the St Asaph site, which has been in operation since 1957.
He blamed competition from other markets, particularly in the Far East, and the strength of the pound.
The spokesman said it was a "sad time" for staff, and Denbighshire Council said it was disappointed at the news.
Gareth Rowlands, the council's cabinet lead member for regeneration, said: "We regret the company's decision, and this marks the end of Pilkington's long association with St Asaph."
But he added: "The council will work with Pilkington and any potential buyer regarding the future development of the site and will provide as much assistance as possible over the coming weeks."