1 Trademark of Trinseo PLC or its affiliates Third Quarter 2025 Financial Results & Fourth Quarter Outlook November 6, 2025

2 Introductions & Disclosure Rules Introductions • Frank Bozich, President & CEO • David Stasse, Executive Vice President & CFO • Bee van Kessel, Senior Vice President, Corporate Finance & Investor Relations Disclosure Rules This presentation may contain forward-looking statements including, without limitation, statements concerning plans, objectives, goals, projections, forecasts, strategies, future events or performance, and underlying assumptions and other statements, which are not statements of historical facts or guarantees or assurances of future performance. Forward-looking statements may be identified by the use of words like “expect,” “anticipate,” “believe,” “intend,” “forecast,” ”estimate,” “see,” “outlook,” “will,” “may,” “might,” “potential,” “likely,” “target,” “plan,” “contemplate,” “seek,” “attempt,” “should,” “could,” “would,” or expressions of similar meaning. Forward-looking statements reflect management’s evaluation of information currently available and are based on our current expectations and assumptions regarding our business, the economy, our current indebtedness, and other future conditions. Because forward-looking statements relate to the future, they are subject to inherent uncertainties, risks and changes in circumstances that are difficult to predict. Factors that might cause future results to differ from those expressed by the forward-looking statements include, but are not limited to, conditions in the global economy and capital markets, including persistent decreased customer demand and the impact of tariffs on global trade relations; our ability to successfully generate cost savings through restructuring and cost reduction initiatives; our ability to successfully execute our business and transformation strategy; increased costs or disruption in the supply of raw materials; deterioration of our credit profile limiting our access to commercial credit; increased energy costs; the timing of, and our ability to complete, a sale of our interest in Americas Styrenics; compliance with laws and regulations impacting our business; any disruptions in production at our chemical manufacturing facilities, including those resulting from accidental spills or discharges; our current and future levels of indebtedness and our ability to service, repay or refinance our indebtedness; our ability to meet the covenants under our existing indebtedness; our ability to generate cash flows from operations and achieve our forecasted cash flows; and those discussed in our Annual Report on Form 10-K, under Part I, Item 1A —"Risk Factors" and elsewhere in our other reports, filings and furnishings made with the U.S. Securities and Exchange Commission from time to time. As a result of these or other factors, our actual results, performance or achievements may differ materially from those contemplated by the forward-looking statements. Therefore, we caution you against relying on any of these forward-looking statements. The forward-looking statements included in this presentation are made only as of the date hereof. We undertake no obligation to publicly update or revise any forward-looking statement as a result of new information, future events or otherwise, except as otherwise required by law. This presentation contains financial measures that are not in accordance with generally accepted accounting principles in the US (“GAAP”) including EBITDA, Adjusted EBITDA, Adjusted Net Income, Adjusted EPS and Free Cash Flow. We believe these measures provide relevant and meaningful information to investors and lenders about the ongoing operating results and liquidity position of the Company. Such measures when referenced herein should not be viewed as an alternative to GAAP measures of performance or liquidity, as applicable. We have provided a reconciliation of these measures to the most comparable GAAP metric alongside of the respective measure or otherwise in the Appendix section and in the accompanying press release.

3 Summary Q3 2025 Results • Net loss of $110 million and EPS of negative $3.05 • Adjusted EBITDA* of $30 million was inclusive of $9 million of unfavorable net timing and negative equity income from Americas Styrenics • Continuation of Q2 supply/demand dynamics with Q3 volumes similar to Q2 volumes * See Appendix for a reconciliation of non-GAAP measures Cash Generation & Liquidity • Cash used in operations of $22 million and capital expenditures of $16 million resulted in Free Cash Flow* of negative $38 million • Third quarter ending cash of $114 million (of which $2 million was restricted) and total liquidity of $346 million Q4 2025 Outlook • Net loss of $170 million to $180 million and Adjusted EBITDA* of $30 million to $40 million, including unfavorable timing of $5 million to $10 million • Free Cash Flow* of approximately $20 million, with a projected available liquidity of approximately $365 million at the end of the year • Assumes continuation of the higher level of demand in our formulated products through November, but an exaggerated seasonal effect in December Key Initiatives • Announced decision to cease virgin MMA production operations at the Rho and Porto Marghera, Italy facilities and repurpose Rho assets for PMMA recycling activities • Announced intention to close the polystyrene production facility in Schkopau, Germany • Continued focus on expansion of our strategic businesses, with 5% growth in our growth platforms and 2% volume growth in our recycled content containing sales year to date

4 5 15 25 35 45 55 65 75 Volume (KT) ABS Imports ABS Exports PMMA Imports PMMA Exports Significant Industry Trade Flow Changes (ABS & PMMA) $204 ~$200 15 25 35 45 55 Volume (KT) ABS Imports ABS Exports PMMA Imports PMMA Exports US Imports and Exports Europe Imports and Exports Source: DataWeb Source: Eurostat PMMA Q2 YoY: Imports (17)% Exports (20)% ABS Q2 YoY: Imports +20% Exports (22)% PMMA Q2 YoY: Imports +3% Exports (7)% ABS Q2 YoY: Imports +9% Exports (3)% • Asian producers pre-loading the sales channel ahead of tariffs • Decreased exports to Mexico and Canada • Asian ABS typically consumed in China being redirected to Europe

5 Q3 2025 Sales and Volume Summary Q3 Net sales in $millions Q3 Volume variances exclude styrene-related sales Third Quarter Volume Drivers: Europe • Lower year over year volumes in Latex Binders paper & board and textile due to mill closures and competitive pressures, partially offset by polystyrene U.S. • Lower year over year volumes from weak demand in Polymer Solutions, mainly driven by the building & construction and automotive industries, partially offset by improvements in PMMA resins and Latex Binders Asia • Flat year over year volumes as improvement in polystyrene was offset by low demand in paper & board and textile Net Sales Global $743 Sales Volume YoY: (4)% Sales Volume YoY: (7)% Sales Volume YoY: (0)% Sales Volume YoY: (3)% Europe $325 U.S. $234 Asia-Pacific $152 Rest of World $33

6 Trinseo Q3 2025 Financial Results Net Sales • Adjusted EBITDA* of $30 million was below prior year mainly driven by $12 million of unfavorable timing impact, lower volumes and unfavorable mix effects, which were partially offset by savings from restructuring initiatives • Equity affiliate income at Americas Styrenics was negative $2 million in the quarter and $6 million below prior year due to an $8 million cost headwind from an unplanned outage * See Appendix for a reconciliation of non-GAAP measures $30 $66 Q3'25 Q3'24 Adjusted EBITDA* ($MM) $743 ($110) $868 ($87) Net Sales Net Loss Net Sales & Net Loss ($MM) Q3'25 Q3'24 Vol Price FX Total (7%) (9%) 2% (14%) ($87) ($3.05) ($58) ($2.47) Adjusted Net Loss Diluted EPS EPS ($) Q3'25 Q3'24

7 Engineered Materials • Adjusted EBITDA was flat versus prior year, with lower medical volumes offsetting higher building and construction and mobility volumes as well as restructuring savings • Year over year improvement in our more formulated products • Volumes of recycled content containing products in Engineered Materials grew 12% year to date $273 $294 Qtr3 2025 Qtr3 2024 Net Sales ($MM) $34 $34 Qtr3 2025 Qtr3 2024 Adjusted EBITDA ($MM) 70 74 Qtr3 2025 Qtr3 2024 Volume (kt) Vol Price FX Total (8%) (1%) 1% (7%)

8 • Adjusted EBITDA was $9 million below prior year mainly due to lower volumes and margins, primarily in paper and board and textile applications in Asia and Europe • Paper and board volumes recovered partially in Asia versus prior quarter • Sales volumes in battery binders were up 27% versus prior year for the quarter as we continue to enhance our portfolio, including new design wins at top customers in anode binder applications Latex Binders $198 $242 Qtr3 2025 Qtr3 2024 Net Sales ($MM) $17 $26 Qtr3 2025 Qtr3 2024 Adjusted EBITDA ($MM) 97 106 Qtr3 2025 Qtr3 2024 Volume (kt) Vol Price FX Total (8%) (12%) 2% (18%)

9 Polymer Solutions • Adjusted EBITDA of $4 million was $19 million below prior year, primarily from $9 million of unfavorable timing as well as lower ABS volumes and unfavorable mix • ABS volumes especially in Europe, continued to be under pressure due to demand weakness and Asian imports at unfavorable economics $271 $331 Qtr3 2025 Qtr3 2024 Net Sales ($MM) $4 $23 Qtr3 2025 Qtr3 2024 Adjusted EBITDA ($MM) 166 167 Qtr3 2025 Qtr3 2024 Volume* (kt) * Volume excludes styrene-related sales Vol Price FX Total (6%) (15%) 3% (18%)

10 Debt and Liquidity (Q3 2025) Cash and Borrowing Debt Maturity Schedule ($ millions) Facilities ($ millions) Revolving Credit Facility* AR Securitization** Cash*** $346MM Combined Cash and Availability under Committed Facilities * Revolving Credit Facility available funds of $237 million is net of $33 million outstanding letters of credit ** AR Securitization Facility borrowing capacity of $7 million *** Cash of $102 million excludes restricted cash of $2 million and cash held by certain unrestricted subsidiaries (as defined under our Credit Agreement) of $10 million $1,956 $443 2025 2026 2027 2028 Term Loans 2029 2L Senior Secured Notes $102 $7 $237

11 2025 Profitability and Cash Generation Outlook • Q4 net loss of $170 million to $180 million and Adjusted EBITDA* of $30 million to $40 million • FY net loss of $408 million to $418 million and Adjusted EBITDA* of $167 million to $177 million • FY cash used in operations of approximately $90 million resulting in Free Cash Flow* of approximately negative $140 million * See Appendix for a reconciliation of non-GAAP measures (in $ millions) FY Estimate Capital Expenditures $(50) Cash Interest $(200) Cash Taxes $(35) Restructuring Cost $(55) Turnarounds $(10) Working Capital / Other $40 Net Cash Expenditures $(310)

12 Appendix

13 Segment Information (in $millions, unless noted) Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 Q4'24 Q1'25 Q2'25 Q3'25 2023 2024 Engineered Materials 73 77 73 76 78 88 74 71 72 76 70 300 310 Latex Binders 112 117 112 106 119 111 106 97 98 92 97 447 434 Polymer Solutions 210 200 192 177 204 174 167 172 174 165 166 779 718 Trade Volume* (kt) 396 393 377 359 402 374 347 340 345 334 333 1,525 1,462 Engineered Materials 305 300 276 275 283 324 294 276 278 293 273 1,157 1,177 Latex Binders 249 255 224 215 241 252 242 218 209 204 198 943 954 Polymer Solutions 442 407 379 347 380 344 331 327 298 287 271 1,576 1,382 Net Sales 996 963 879 837 904 920 868 821 785 784 743 3,675 3,513 Engineered Materials 0 23 15 7 10 32 34 27 26 31 34 46 102 Latex Binders 24 23 18 18 26 26 26 19 24 17 17 83 95 Polymer Solutions 21 15 6 9 29 16 23 17 44 5 4 50 86 Americas Styrenics 18 13 19 13 6 16 4 (10) (2) 8 (2) 62 15 Corporate (26) (17) (17) (27) (26) (23) (20) (26) (28) (20) (22) (87) (95) Adjusted EBITDA** 36 57 41 20 45 67 66 26 65 42 30 154 204 Adj EBITDA Variance Analysis Net Timing** Impacts - Fav/(Unfav) Engineered Materials (7) (8) (6) 5 (7) 0 1 (1) (0) (1) (1) (17) (6) Latex Binders 1 (1) (1) 0 2 (1) 1 0 1 (2) (1) (1) 2 Polymer Solutions 4 (6) 3 (4) 18 (9) 2 (9) 8 (8) (7) (3) 2 Net Timing*** Impacts - Fav/(Unfav) (2) (16) (4) 1 13 (10) 3 (9) 9 (10) (9) (20) (2) *Trade volume excludes styrene-related sales **See this Appendix for a reconciliation of non-GAAP measures ***Net Timing is the difference between Raw Material Timing and Price Lag. Raw Material Timing represents the timing of raw material cost changes flowing through cost of goods sold versus current pricing. Price Lag represents the difference in revenue between the current contractual price and the current period price.

14 (in $millions, unless noted) Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 Q4'24 Q1'25 Q2'25 Q3'25 2023 2024 Net Loss (48.9) (349.0) (38.4) (265.0) (75.5) (67.8) (87.3) (117.9) (79.0) (105.5) (109.7) (701.3) (348.5) Interest expense, net 38.3 40.2 46.6 63.3 63.0 64.7 72.3 67.5 66.6 69.5 70.6 188.4 267.5 Provision for (benefit from) income taxes (16.7) (25.1) (17.7) 127.9 5.4 20.3 3.4 1.4 6.6 2.5 8.3 68.4 30.5 Depreciation and amortization 56.0 52.5 38.2 74.4 45.0 46.6 48.3 70.3 36.0 59.8 56.4 221.2 210.2 EBITDA 28.7 (281.4) 28.7 0.6 37.9 63.8 36.7 21.3 30.2 26.3 25.6 (223.3) 159.7 Other items 3.6 2.6 7.2 8.0 1.3 2.5 0.9 1.7 2.3 2.9 1.1 21.4 6.4 Restructuring and other charges 3.7 1.5 13.8 12.5 9.4 4.0 28.5 2.8 7.4 10.8 3.7 31.5 44.7 Loss on financing transactions - - - - - - - - 24.9 1.6 - - - Net gain on disposition of businesses and assets - (16.3) (9.3) - (3.6) (3.5) - - - - - (25.6) (7.1) Acquisition transaction and integration net costs - 0.1 - (1.5) - - - - - - - (1.4) - Goodwill impairment charges - 349.0 - - - - - - - - - 349.0 - Asset impairment charges or write-offs 0.3 1.3 0.5 0.6 - - - - - - - 2.7 - Adjusted EBITDA 36.3 56.8 40.9 20.2 45.0 66.8 66.1 25.8 64.8 41.6 30.4 154.3 203.7 Adjusted EBITDA to Adjusted Net Income Adjusted EBITDA 36.3 56.8 40.9 20.2 45.0 66.8 66.1 25.8 64.8 41.6 30.4 154.3 203.7 Interest expense, net 38.3 40.2 46.6 63.3 63.0 64.7 72.3 67.5 66.6 69.5 70.6 188.4 267.5 Provision for (benefit from) income taxes - Adjusted (20.0) 34.8 (18.6) 12.1 4.2 5.9 3.5 6.4 1.2 2.8 3.9 8.3 20.0 Depreciation and amortization - Adjusted 53.3 49.5 49.2 50.0 46.3 47.9 47.8 46.4 45.5 44.9 42.6 202.0 188.4 Adjusted Net Income (Loss) (35.3) (67.7) (36.3) (105.2) (68.5) (51.7) (57.5) (94.5) (48.5) (75.6) (86.7) (244.4) (272.2) Wtd Avg Shares - Diluted (000) 35,032 35,153 35,191 35,200 35,250 35,307 35,360 35,403 35,513 35,674 35,959 35,274 35,330 Adjusted EPS - Diluted ($) (1.01) (1.93) (1.03) (2.99) (1.94) (1.46) (1.63) (2.67) (1.37) (2.12) (2.41) (6.93) (7.70) Adjustments by Statement of Operations Caption Loss on extinguishment of long-term debt - - - - - - 0.6 - 0.2 - - - 0.6 Cost of sales - 1.2 0.4 5.5 - - - - - - - 7.1 - SG&A 7.3 (12.1) 15.4 13.5 7.1 6.5 29.6 4.5 34.4 16.0 4.8 24.1 47.7 Impairment and other charges 0.3 349.1 - 0.6 - - - - - - - 350.0 - Acquisition purchase price hedge (gain) loss - - - - - - - - - - - - - Other expense (income), net - - (3.6) - - (3.5) (0.8) - - (0.7) - (3.6) (4.3) Total EBITDA Adjustments 7.6 338.2 12.2 19.6 7.1 3.0 29.4 4.5 34.6 15.3 4.8 377.6 44.0 Free Cash Flow Reconciliation Cash provided by (used in) operating activities 45.4 56.5 29.3 17.5 (66.2) (41.9) 8.8 85.1 (110.3) 6.8 (21.6) 148.7 (14.2) Capital expenditures (21.8) (13.8) (13.5) (20.6) (15.7) (14.2) (12.2) (21.2) (8.7) (9.8) (16.5) (69.7) (63.3) Free Cash Flow 23.6 42.7 15.8 (3.1) (81.9) (56.1) (3.4) 63.9 (119.0) (3.0) (38.1) 79.0 (77.5) US GAAP to Non-GAAP Reconciliation NOTE: For definitions of non-GAAP measures as well as descriptions of current period reconciling items from Net Income (Loss) to Adjusted EBITDA and to Adjusted Net Income (Loss), refer to the accompanying press release furnished as Exhibit 99.1 to our Form 8-K dated November 6, 2025. Totals may not sum due to rounding.

15 US GAAP to Non-GAAP Reconciliation NOTE: For definitions of non-GAAP measures as well as descriptions of current period reconciling items from Net Income (Loss) to Adjusted EBITDA and to Adjusted Net Income (Loss), refer to the accompanying press release furnished as Exhibit 99.1 to our Form 8-K dated November 6, 2025. Totals may not sum due to rounding. Profitability Outlook Cash Flow Outlook