Business Combination Prospectus (Form 425)

Filed by Huntsman Corporation

Pursuant to Rule 425 of the Securities Act of 1933

and deemed filed pursuant to Rule 14a-12

of the Securities Exchange Act of 1934

Subject Company: Huntsman Corporation

Commission File No.: 001-32427

The following are communications relating to the proposed transaction between Olin Corporation and Huntsman Corporation provided to employees of Huntsman Corporation on June 16, 2026.

CEO Merger Announcement

EMAIL DETAILS:

Subject: Huntsman & Olin - A Merger of Equals
Second Subject Line: A Message from Peter Huntsman

EMAIL COPY:

June 16, 2026

Dear Associates,

Today marks an important and significant milestone in our company's history. Our Board of Directors has unanimously approved an agreement to merge Huntsman with Olin Corporation in an all-stock transaction.

This is a meaningful step forward that brings together two strong companies with proud legacies, complementary strengths and values that, when combined, will create a stronger company as we are able to compete more effectively in a global market where all too often, we are competing against countries as often as companies.

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The merger will create a $12B chemical company that will be able to compete more effectively due to our supply chain integration. The combined company will be producing our own raw materials that today we purchase on the open market.

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Our size will enable us to weather global market changes that have only increased in recent years. We will be more deeply integrated in our supply chains in North America and Europe and have greater opportunities to grow in Asia.

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We will create more than $400MM in synergies. We'll do this by eliminating duplicate corporate costs, improving our raw material sourcing and integrating our supply chains, and capitalizing on our respective best practices and technologies.

In short, our size and integration will make us better able to prosper in today's highly competitive and global markets.

While this is the strategic rationale behind the merger, it is important to remember that today's announcement is the beginning of a process-not the completion of one. There are still important steps ahead, including regulatory review and shareholder approval. While timelines can change, we currently believe the process may run until sometime within the first half of 2027.

I encourage you to listen to our shareholder webcast today at 8 a.m. ET and by attending an internal local or virtual town hall for which you'll receive a calendar invitation soon. These town halls will be held by local leaders, and I hope you will attend.

While we await shareholder and government approvals between now and closing, our priorities will remain unchanged. The safety and reliability of our operations is our top priority.

Our internal communications and management will communicate our progress and any changes as they occur. Let's not be distracted by rumors or speculation.

Upon completion, we will be a stronger and more viable company, better able to compete, grow, and expand opportunities for our associates, customers, and shareholders. This puts our company in a much stronger position than where we otherwise would be.

I look forward to updating you on a regular basis.

Sincerely,

Peter R. Huntsman
Chairman, President and CEO
Huntsman Corporation

Additional Information and Where to Find It

This communication may be deemed to be solicitation material in respect of the proposed transaction between Olin Corporation ("Olin") and Huntsman Corporation ("Huntsman"). In connection with the proposed transaction, Olin and Huntsman intend to file relevant materials with the United States Securities and Exchange Commission (the "SEC"), including, among other filings, an Olin registration statement on Form S-4 in connection with the proposed issuance of shares of Olin's common stock pursuant to the proposed transaction, which Form S-4 will include a joint proxy statement/prospectus of Olin and Huntsman, which after the registration statement is declared effective by the SEC, will be mailed to shareholders of Olin and stockholders of Huntsman seeking their approval of their respective transaction-related proposals. INVESTORS AND STOCKHOLDERS OF OLIN AND HUNTSMAN ARE URGED TO READ ALL RELEVANT DOCUMENTS FILED WITH THE SEC IN THEIR ENTIRETY, INCLUDING THE REGISTRATION STATEMENT AND THE JOINT PROXY STATEMENT/PROSPECTUS, AS EACH MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, BECAUSE THEY CONTAIN OR WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION, THE PARTIES TO THE PROPOSED TRANSACTION AND ANY SOLICITATION. This communication is not a substitute for the registration statement, the joint proxy statement/prospectus or any other document that Olin or Huntsman may file with the SEC and send to their respective shareholders and stockholders in connection with the proposed transaction. Investors and securityholders will be able to obtain free copies of the registration statement and the joint proxy statement/prospectus, as each may be amended or supplemented from time to time, and other relevant documents filed with the SEC by Olin and Huntsman (when they become available) from the SEC's website at www.sec.gov, on Olin's website at www.Olin.com under the tab "Investors" and under the heading "SEC Filings" and on Huntsman's website at www.Huntsman.com under the tab "Investors" and under the heading "Financials" and subheading "SEC filings."

Participants in the Solicitation

Olin, Huntsman, their respective directors, executive officers and certain other members of management and employees, under SEC rules, may be deemed to be "participants" in the solicitation of proxies from Olin's shareholders and Huntsman's stockholders in connection with the proposed transaction. Information about Olin's directors and executive officers is set forth in Olin's Proxy Statement on Schedule 14A for its 2026 Annual Meeting of shareholders, which was filed with the SEC on March 20, 2026, its Annual Report on Form 10-K for the year ended December 31, 2025, which was filed with the SEC on February 20, 2026, its Current Report on Form 8-K, which was filed with the SEC on April 30, 2026, and subsequent statements of changes in beneficial ownership on file with the SEC, including the Initial Statements of Beneficial Ownership on Form 3, Statements of Change in Ownership on Form 4 or Annual Statements of Beneficial Ownership on Form 5 on file with the SEC, including filings made on March 20, 2026, May 5, 2026, May 19, 2026 and June 3, 2026. Information about Huntsman's directors and executive officers is set forth in the Huntsman Proxy Statement on Schedule 14A for its 2026 Annual Meeting of stockholders, which was filed with the SEC on March 16, 2026, its Annual Report on Form 10-K for the year ended December 31, 2025, which was filed with the SEC on February 18, 2026, its Current Report on Form 8-K, which was filed with the SEC since May 1, 2026, and subsequent statements of changes in beneficial ownership on file with the SEC, including the Initial Statement of Beneficial Ownership on Form 3, Statements of Change in Ownership on Form 4 or Annual Statements of Beneficial Ownership on Form 5 on file with the SEC, including filings made on June 3, 2026.

No Offer or Solicitation

This communication does not constitute an offer to sell or the solicitation of an offer to buy or exchange any securities or a solicitation of any vote or approval in any jurisdiction. It does not constitute a prospectus or prospectus equivalent document. No offering of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the U.S. Securities Act of 1933, as amended.

Additional information concerning the interests of potential participants in the solicitation of proxies in connection with the proposed transaction, which may, in some cases, be different than those of Olin's shareholders or Huntsman's stockholders generally, will be set forth in the registration statement, the joint proxy statement/prospectus and other relevant materials to be filed with the SEC relating to the proposed transaction. You may obtain these documents (when they become available) free of charge through the website maintained by the SEC at http://www.sec.gov and from the Olin or Huntsman websites described above.

Cautionary Statement Regarding Forward-Looking Statements

This communication contains "forward-looking statements". These statements relate to analyses and other information that are based on management's current beliefs, certain assumptions and forecasts made by management, and current expectations, estimates and projections. Such forward-looking statements include statements regarding the proposed combination between Olin and Huntsman, the future results of the combined company and the benefits anticipated to be realized from the proposed combination, the impact of the proposed transaction on the combined company's business, projections as to the amount and timing of synergies and the closing date for the proposed transaction, and other uncertainties and contingencies in connection with the foregoing. The statements contained in this communication that are not statements of historical facts may include "forward looking statements" as defined in the Private Securities Litigation Reform Act of 1995. We have used the words "anticipate," "intend," "may," "expect," "believe," "should," "plan," "outlook," "project," "estimate," "forecast," "optimistic," "target" and variations of such words and similar expressions in this communication to identify such forward-looking statements.

The reader is cautioned not to rely on these forward-looking statements. These statements are based on current expectations of future events. If underlying assumptions prove inaccurate or known or unknown risks or uncertainties materialize, actual results could vary materially from these forward-looking statements. Risks and uncertainties include, but are not limited to: (i) the risk that the proposed transaction may not achieve some or all of the anticipated benefits and that the proposed transaction may not be completed in a timely manner or at all; (ii) the failure to receive, on a timely basis or otherwise, the required approvals of the proposed transaction by Olin's shareholders or Huntsman's stockholders; (iii) the possibility that any or all of the various conditions to the consummation of the proposed transaction may not be satisfied or waived, including the failure to receive any required regulatory approvals from any applicable governmental entities (or any conditions, limitations or restrictions placed on such approvals); (iv) the possibility that competing offers or acquisition proposals may be made; (v) the occurrence of any event, change or other circumstance that could give rise to the termination of the merger agreement relating to the proposed transaction; (vi) the effect of the announcement or pendency of the proposed transaction on Olin's or Huntsman's ability to attract, motivate or retain key executives and associates, their ability to maintain relationships with customers, vendors, service providers and others with whom they do business, or their operating results and business generally; (vii) risks related to the proposed transaction diverting management's attention from Olin's and Huntsman's ongoing business operations; (viii) the risk of stockholder litigation in connection with the proposed transaction, including resulting expense or delay; (ix) business, industry and operational risks applicable to Olin and/or Huntsman, including (a) sensitivity to economic, business and market conditions in the United States and overseas, including economic instability or a downturn in the sectors served by Olin and/or Huntsman; (b) declines in average selling prices for Olin's and/or Huntsman's products and the supply/demand balance for Olin's and/or Huntsman's products, including the impact of excess industry capacity; (c) unsuccessful execution of Olin's and/or Huntsman's operating models; (d) failure to control costs and inflation impacts or failure to achieve targeted cost reductions; (e) availability of and/or higher-than-expected costs of raw material, energy, transportation, and/or logistics; (f) Olin's and/or Huntsman's reliance on a limited number of suppliers for specified feedstock and services and their reliance on third-party transportation; (g) the occurrence of unexpected manufacturing interruptions and outages, including those occurring as a result of labor disruptions and production hazards; (h) exposure to physical risks associated with climate-related events or increased severity and frequency of severe weather events; (i) the failure or an interruption, including cyber-attacks, of Olin's and/or Huntsman's information technology systems, including risks from the rapid evolution and increased adoption of artificial intelligence technologies that may intensify cybersecurity risks and enable new or augment existing attack techniques and the potential for intellectual property infringement or unintentional disclosure of proprietary or confidential information through artificial intelligence tools; (j) risks associated with Olin's and/or Huntsman's international sales and operations, including economic, political or regulatory changes; (k) weak industry conditions affecting Olin's and/or Huntsman's ability to comply with the financial maintenance covenants in its debt agreements; (l) Olin's and/or Huntsman's indebtedness and debt service obligations; (m) failure to identify, attract, develop, retain and motivate qualified employees throughout the respective organizations and ability to manage executive officer and other key senior management transitions; (n) adverse conditions in the credit and capital markets, limiting or preventing Olin's and/or Huntsman's ability to borrow or raise capital; (o) Olin's and/or Huntsman's inability to complete future acquisitions or joint venture transactions or successfully integrate them into the business; (p) the effects of any declines in global equity markets on asset values and any declines in interest rates or other significant assumptions used to value the liabilities in, and funding of, Olin's and/or Huntsman's pension plans; (q) Olin's and/or Huntsman's long-range plan assumptions not being realized, causing a non-cash impairment charge of long-lived assets; (r) exposure to risks associated with the creditworthiness of Olin's and/or Huntsman's key suppliers, customers and business partners and reductions in demand for their customers' products; (s) failure to develop new products, processes or applications, or failure to keep pace with evolving technological innovations in end-use markets; (t) inability to protect patents and trade secrets or enforce intellectual property rights, particularly in countries where effective intellectual property laws and judicial systems may be unavailable; (u) conflicts, military actions, terrorist attacks, political events, public health crises and general instability, along with increased security regulations, that could adversely affect Olin and/or Huntsman's business; and (v) legal, environmental and regulatory risks, including (a) changes in, or failure to comply with, legislation or government regulations or policies, including changes regarding Olin's and/or Huntsman's ability to manufacture or use certain products and changes within the international markets in which Olin and/or Huntsman operate; (b) new regulations or public policy changes regarding the transportation of hazardous chemicals and the security of chemical manufacturing facilities; (c) unexpected outcomes from legal or regulatory claims and proceedings; (d) costs and other expenditures in excess of those projected for environmental investigation and remediation or other legal proceedings; (e) various risks associated with Olin's Lake City U.S. Army Ammunition Plant contract and performance under other governmental contracts; and (f) compliance with data privacy regulations, including the General Data Protection Regulation (GDPR) and other applicable data privacy laws, which could result in substantial fines, penalties and legal liability.

All of Olin's and Huntsman's forward-looking statements should be considered in light of these factors. In addition, other risks and uncertainties not presently known to Olin or Huntsman or that Olin or Huntsman consider immaterial could affect the accuracy of the forward-looking statements. These statements are not guarantees of future performance and involve certain risks, uncertainties, and assumptions, which are difficult to predict and many of which are beyond the control of Olin and/or Huntsman. Therefore, actual outcomes and results may differ materially from those matters expressed or implied in such forward-looking statements. A further list and descriptions of these risks, uncertainties, and other factors can be found in Olin's filings with the SEC, including its most recent Annual Report on Form 10-K and subsequent Quarterly Reports on Form 10-Q and other filings, available at the website maintained by the SEC at http://www.sec.gov, https://olin.com or on request from Olin and in Huntsman's filings with the SEC, including its most recent Annual Report on Form 10-K and subsequent Quarterly Reports on Form 10-Q and other filings, available at the website maintained by the SEC at http://www.sec.gov, https://www.huntsman.com or on request from Huntsman. Any forward-looking statement made in this communication speaks only as of the date of this communication. Neither Olin nor Huntsman undertake any obligation to update publicly any forward-looking statements, or any other information in this communication whether as a result of future events, new information or otherwise, or to correct any inaccuracies or omissions in them which become apparent. All forward-looking statements in this communication are qualified in their entirety by this cautionary statement.