The company has said the initiative supports the group's business, which is based on a cycle of sustainable development.
Soporcel executive director António Redondo said: "We look forward to co-operating with Two Sides, which I believe is an industry-wide initiative that is completely necessary."
The NAPM's campaign has been launched in a bid to show that print and paper is an environmentally sustainable medium.
Earlier this month, the association said it would bolster its efforts to get printers on board.
Two Sides was launched in October 2008 and aims to dispel environmental misconceptions around print and paper.
It has so far largely been supported by suppliers and clients of the industry, which includes all the major mill and merchant groups, UPM, Sun Chemical, Fuji, Haymarket Publishing, Duplo and Trinity Mirror Printing.
Printers can join the campaign for £25 per million of UK turnover, although a minimum of £150 is required.
Soporcel becomes latest to back Two Sides initiative
Uncoated fine paper manufacturer Portucel Soporcel has become the latest company to announce its support for the National Association of Paper Merchant's (NAPM) Two Sides campaign.
