Shares of Sylvamo Corporation (SLVM) plummeted more than 5% in premarket trading on Monday, despite the company reporting better-than-expected third-quarter results. The steep decline was primarily driven by Sylvamo's guidance for a weaker fourth quarter, as the company expects to face headwinds from unfavorable pricing and mix changes in its pulp and paper businesses.

For the third quarter ended September 30, Sylvamo reported adjusted operating earnings of $2.44 per diluted share, surpassing analysts' estimates of $2.18. Net sales also rose to $965 million, exceeding expectations of $960.5 million. The company's performance was bolstered by strong demand and disciplined cost management across its core segments.

However, Sylvamo's outlook for the fourth quarter overshadowed its solid third-quarter results. The company expects adjusted EBITDA to range between $150 million and $165 million in Q4, reflecting an anticipated unfavorable impact of $20 million to $25 million from price and mix changes, primarily due to pulp and paper price decreases in certain regions.