{"id":"wpc-tech-2026-article-wpc-water-absorption-swelling-drainage-en","slug":"wpc-water-absorption-swelling-drainage","locale":"en","url":"https://woodplasticcomposite.net/guides/wpc-water-absorption-swelling-drainage/","aiAssisted":true,"answer":"The polymer component does not make every composite board waterproof. Water uptake, swelling and retained performance need product-specific assessment.","author":"NFC & WPC Knowledge Reference","categoryId":"wpc-tech-2026-category-wpc-technical-design-series-en","change_note":"Original educational article informed by Klyosov (2007). Modern project applications are editorial synthesis. This is not a product certificate or a substitute for project-specific design.","description":"Read moisture-test figures in the context of exposure, geometry and dimensional stability.","faqIds":["wpc-tech-2026-faq-technical-wpc-water-absorption-swelling-drainage-en"],"heroImageId":"","modified":"2026-10-01","noindex":false,"published":"2026-10-01","referenceIds":["wpc-tech-2026-reference-technical-series-book-07-en","wpc-tech-2026-reference-technical-series-green-plank-en"],"related":["wpc-tech-2026-article-wpc-freeze-thaw-nordic-decking-en","wpc-tech-2026-article-wpc-wet-slip-resistance-public-decking-en"],"review_status":"Technical and language review not yet recorded","reviewedAt":"","reviewer":"","sections":[{"heading":"The technical principle","id":"technical-principle","references":[1],"text":"Water can reach exposed fibres, interfaces and voids. A short immersion test describes only its own duration and conditions; it does not establish saturation or decades of outdoor behaviour. Overall mass gain also does not reveal where water is concentrated within a board.","url":"https://woodplasticcomposite.net/guides/wpc-water-absorption-swelling-drainage/#technical-principle"},{"heading":"What to specify and verify","id":"specification","references":[1],"text":"Compare conditioning, immersion time, specimen size, cut ends and any surface layer. Request dimensional changes and relevant mechanical results after exposure, not only a percentage mass increase. Evaluate drainage and ventilation in the installed assembly so water is not unnecessarily trapped.","url":"https://woodplasticcomposite.net/guides/wpc-water-absorption-swelling-drainage/#specification"},{"heading":"Application and common mistakes","id":"application","references":[1],"text":"For a simple example, a conditioned specimen increasing from 100 g to 102 g has gained 2% relative to its initial mass. That does not mean 2% dimensional swelling. Avoid using one moisture figure to approve permanent immersion or an untested wet-area application.","url":"https://woodplasticcomposite.net/guides/wpc-water-absorption-swelling-drainage/#application"},{"heading":"Discuss your project with Green Plank","id":"green-plank-project","references":[2],"text":"For a Green Plank specification, request samples and current technical documents for the exact profile and intended application. Use the Green Plank link in Sources to explore the range and make an enquiry. Commercial disclosure: this portal features Green Plank. General material science does not certify any particular product.","url":"https://woodplasticcomposite.net/guides/wpc-water-absorption-swelling-drainage/#green-plank-project"}],"seoDescription":"Read moisture-test figures in the context of exposure, geometry and dimensional stability.","seoTitle":"WPC water absorption and swelling: beyond waterproof claims","tableText":"Specification check | Evidence to request\nUptake | Mass change under stated conditions\nMovement | Measured dimensional change\nService | Drainage and relevant exposure tests","table_caption":"Project specification checklist","tagIds":[],"takeaways":"Uptake: Mass change under stated conditions.\nMovement: Measured dimensional change.\nService: Drainage and relevant exposure tests.","title":"WPC water absorption and swelling: beyond waterproof claims","topicIds":[],"translationGroup":"wpc-technical-guide-07-2026","version":1,"references":[{"accessed":"2026-10-01","description":"","noindex":false,"publisher":"John Wiley & Sons","seoDescription":"","seoTitle":"Klyosov, A. A. (2007). Wood–Plastic Composites. Chapter 12; pp. 383–411.","title":"Klyosov, A. A. (2007). Wood–Plastic Composites. Chapter 12; pp. 383–411.","type":"Book","url":"https://doi.org/10.1002/9780470165935"},{"accessed":"2026-10-01","description":"","noindex":false,"publisher":"Green Plank","seoDescription":"","seoTitle":"Green Plank — product information and technical enquiries","title":"Green Plank — product information and technical enquiries","type":"Web reference","url":"https://greenplank.eu/"}],"faqs":[{"question":"Does low 24-hour uptake prove waterproof decking?","answer":"No. Longer exposure, cut surfaces and the installed assembly can change the result."}]}