1 Trademark of Trinseo PLC or its affiliates Third Quarter 2024 Financial Results & Fourth Quarter Outlook November 6, 2024

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,” “outlook,” “will,” “may,” “might,” “see,” “tend,” “assume,” “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, our ability to successfully implement proposed restructuring initiatives, including the closure of certain plants and product lines, and to successfully generate cost savings through restructuring and cost reduction initiatives; our ability to successfully execute our business and transformation strategy; the timing of, and our ability to complete, the sale of our interest in Americas Styrenics; increased costs or disruption in the supply of raw materials; deterioration of our credit profile limiting our access to commercial credit; increased energy costs; 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; conditions in the global economy and capital markets; our current and future levels of indebtedness and ability to service our debt; 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 press release 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 2024 Results • Net loss of $87 million and EPS of negative $2.47; included pre-tax restructuring and other charges of $26 million related to recently announced restructuring initiatives • Adjusted EBITDA* of $66 million, including a $3 million favorable impact from net timing, was $25 million higher than prior year * See Appendix for a reconciliation of non-GAAP measures Cash Generation & Liquidity • Q3 cash provided by operations of $9 million led to Free Cash Flow* of negative $3 million, which included a $16 million decrease in trade working capital • Q3 ending cash of $167 million, of which $2 million is restricted, with $177 million of additional available liquidity under two committed financing facilities • Q3 cash benefit of $12 million from election of the payment-in-kind option Q4 2024 Outlook • Net loss of $81 million to $71 million • Adjusted EBITDA* of $40 million to $50 million • Sequentially lower profitability driven by year-end seasonality, with cash flow expected to turn positive due to seasonal working capital improvements Key Initiatives • Announced restructuring initiatives focused on the consolidation of business management and support function roles, which are expected to result in cost savings of $25 million in 2025 and full run rate savings of $30 million by the end of 2026 • Announced decision to exit virgin polycarbonate production at the Stade, Germany production facility • Sales of recycled-content-containing products increased 57% year-to-date

4 Europe $406 U.S. $255 Asia-Pacific $176 Rest of World $31 Q3 2024 Sales and Volume Summary Net sales in $millions Volume variances exclude styrene-related sales Europe • Lower year-over-year volumes from Polystyrene portfolio optimization to increase profitability and decrease working capital, along with weak demand in building and construction and appliances U.S. • Higher year-over-year volumes driven by Copolymers due to prior year destocking, and higher graphical paper and CASE in Latex Binders Asia • Lower year-over-year volumes from Polystyrene portfolio optimization, along with weak home appliances demand • Lower volumes in Latex Binders due to weak domestic demand in China • Higher volumes in Engineered Materials driven by strength in consumer electronics applications Net Sales Global $868 Sales Volume YoY: (8%) Sales Volume YoY: (7%) Sales Volume YoY: (22%) Sales Volume YoY: +16%

5 Trinseo Q3 2024 Financial Results $868 ($87) $879 ($38) Net Sales Net Income Net Sales & Net Income ($MM) Q3'24 Q3'23 ($2.47) ($1.62) ($1.09) ($1.03) Diluted EPS Adj EPS* EPS ($) Q3'24 Q3'23 $66 $41 Q3'24 Q3'23 Adjusted EBITDA* ($MM) Vol Price FX Total (8%) 7% (0%) (1%) Net Sales • Significant year-over-year Adjusted EBITDA improvement driven by restructuring actions, lower natural gas hedge losses, continued moderation of European input costs and a favorable net timing variance • This was partially offset by lower equity affiliate income at Americas Styrenics driven by a $10 million negative impact from unplanned outages during the quarter * See Appendix for a reconciliation of non-GAAP measures

6 Engineered Materials • Year-over-year volume increase driven by higher sales of compounds for consumer electronics applications, which improved 36% versus prior year • Adjusted EBITDA was $20 million above prior year due to higher sales, moderating input costs, and a favorable timing variance $207 $186 Q3'24 Q3'23 Net Sales ($MM) Vol Price FX Total 6% 6% (0%) 12% $25 $5 Q3'24 Q3'23 Adjusted EBITDA ($MM) 49 47 Q3'24 Q3'23 Volume (kt)

7 • Year-over-year volume decline from Asia and Europe paper and carpet applications due to weak demand; regional and application mix improved, in line with our strategy • Adjusted EBITDA was $8 million above prior year due to higher margin from the exit of styrene production in Terneuzen as well as a favorable net timing variance • Sales volumes to CASE applications increased 6% year-over-year and accounted for 12% of total segment volumes for the second consecutive quarter Latex Binders $242 $224 Q3'24 Q3'23 Net Sales ($MM) $26 $18 Q3'24 Q3'23 Adjusted EBITDA ($MM) 106 112 Q3'24 Q3'23 Volume* (kt) Vol Price FX Total (4%) 12% (0%) 8% *Volumes exclude styrene-related sales

8 Plastics Solutions • Adjusted EBITDA was $11 million above prior year due to higher margin from the exit of styrene production in Terneuzen and higher fixed cost absorption related to building inventory ahead of the Stade polycarbonate closure • Fixed cost absorption expected to reverse in the fourth quarter $268 $259 Q3'24 Q3'23 Net Sales ($MM) $28 $17 Q3'24 Q3'23 Adjusted EBITDA ($MM) 102 100 Q3'24 Q3'23 Volume* (kt) Vol Price FX Total (1%) 4% (0%) 3% *Volumes exclude styrene-related sales

9 Polystyrene • Lower year-over-year volumes due to an intentional reduction of low-margin sales to optimize plant operations and sales mix, along with weak demand in building and construction and appliances • Adjusted EBITDA was $5 million above prior year due to higher margins and lower fixed costs from the exit of styrene production in Terneuzen • 88% year-to-date increase in sales volume of recycled-content-containing polystyrene with a significant margin premium $151 $210 Q3'24 Q3'23 Net Sales ($MM) $4 ($1) Q3'24 Q3'23 Adjusted EBITDA ($MM) 90 118 Q3'24 Q3'23 Volume* (kt) Vol Price FX Total (35%) 7% (0%) (28%) *Volumes exclude styrene-related sales

10 $115 $1,794 $447 2024 2025 Senior Notes 2026 2027 2028 Term Loans 2029 Senior Notes $167 $75 $102 Debt and Liquidity Overview (as of September 30, 2024) Debt Maturity Schedule ($millions) May April Cash and Borrowing Facilities ($millions)* Revolving Credit Facility AR Securitization Cash** $344MM Combined Cash and Availability under Committed Facilities *2026 Revolving Credit Facility available funds of $102.0 million (net of $10.3 million outstanding letters of credit), as well as the Accounts Receivable Securitization Facility with borrowing capacity of $75 million. **Included restricted cash of $2.3 million September

11 (In $millions) Full Year 2024 Adjusted EBITDA* 218 - 228 Capital Expenditures (65) Cash Interest (200) Cash Taxes (20) Restructuring Cost (45) Turnarounds (10) Working Capital / Other ~40 Free Cash Flow* ~(80) 2024 Profitability and Cash Generation Outlook FY net loss of $312 million to $302 million and Adjusted EBITDA* of $218 million to $228 million Q4 net loss of $81 million to $71 million and Adjusted EBITDA* of $40 million to $50 million • Sequentially lower profitability due to year-end seasonality • Fixed cost absorption benefit in Q3 related to Stade polycarbonate closure expected to reverse in Q4 FY cash used in operations of approximately $15 million resulting in Free Cash Flow* of approximately negative $80 million • Q4 Free Cash Flow* of approximately $60 million; sequentially higher due to seasonal working capital improvements * See Appendix for a reconciliation of non-GAAP measures

12 Appendix

13 (in $millions, unless noted) Q1'22 Q2'22 Q3'22 Q4'22 Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 2022 2023 Engineered Materials 60 60 50 41 46 50 47 51 50 60 49 212 194 Latex Binders 132 138 132 117 112 117 112 106 119 111 106 520 447 Plastics Solutions 134 120 100 102 109 105 100 96 108 102 102 457 409 Polystyrene 165 141 124 134 129 122 118 107 124 101 90 564 475 Trade Volume* (kt) 493 460 407 394 396 393 377 359 402 374 347 1,753 1,525 Engineered Materials 295 301 243 205 206 206 186 190 189 230 207 1,044 789 Latex Binders 309 360 343 255 249 255 224 215 241 252 242 1,267 943 Plastics Solutions 418 380 305 278 300 282 259 240 266 263 268 1,382 1,081 Polystyrene 364 384 287 237 241 220 210 192 208 175 151 1,272 863 Net Sales 1,387 1,426 1,178 975 996 963 879 837 904 920 868 4,966 3,675 Engineered Materials 35 34 8 (5) (12) 12 5 (0) 4 25 25 72 5 Latex Binders 31 32 14 16 24 23 18 18 26 26 26 93 83 Plastics Solutions 71 49 (32) (12) 24 24 17 16 23 16 28 76 81 Polystyrene 45 32 (25) 4 9 2 (1) 0 13 7 4 56 10 Americas Styrenics 22 39 23 18 18 13 19 13 6 16 4 102 62 Corporate (27) (21) (24) (16) (26) (17) (17) (27) (26) (23) (20) (88) (87) Adjusted EBITDA** 178 164 (37) 6 36 57 41 20 45 67 66 312 154 Adj EBITDA Variance Analysis Net Timing** Impacts - Fav/(Unfav) Engineered Materials (0) 0 (1) (3) (7) (9) (6) 5 (7) 2 1 (3) (17) Latex Binders 6 1 1 (3) 1 (1) (1) 0 2 (1) 1 5 (1) Plastics Solutions 15 14 (8) (4) (1) (2) 0 1 9 (7) 0 17 (1) Polystyrene 10 17 (16) (9) 5 (4) 3 (5) 9 (4) 1 2 (1) Net Timing*** Impacts - Fav/(Unfav) 32 33 (24) (19) (2) (16) (4) 1 13 (10) 3 21 (20) *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. Segment Information

14 (in $millions, unless noted) Q1'22 Q2'22 Q3'22 Q4'22 Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 2022 2023 Engineered Materials 60 60 50 41 46 50 47 51 50 60 49 212 194 Latex Binders 132 138 132 117 112 117 112 106 119 111 106 520 447 Plastics Solutions 134 120 100 102 109 105 100 96 108 102 102 457 409 Polystyrene 165 141 124 134 129 122 118 107 124 101 90 564 475 Trade Volume* (kt) 493 460 407 394 396 393 377 359 402 374 347 1,753 1,525 Engineered Materials 295 301 243 205 206 206 186 190 189 230 207 1,044 789 Latex Binders 307 354 341 255 248 254 222 215 241 252 242 1,256 939 Plastics Solutions 396 362 293 271 290 272 246 231 266 263 268 1,323 1,038 Polystyrene 318 312 248 216 209 193 175 166 208 175 151 1,093 743 Feedstocks 70 97 53 28 43 37 50 35 - - - 249 166 Net Sales 1,387 1,426 1,178 975 996 963 879 837 904 920 868 4,966 3,675 Engineered Materials 35 34 8 (5) (12) 12 5 (0) 4 25 25 72 5 Latex Binders 30 29 31 20 26 25 23 19 26 26 26 111 93 Plastics Solutions 69 46 (15) (9) 26 25 22 16 23 16 28 91 89 Polystyrene 45 23 19 12 16 6 9 2 13 7 4 99 33 Feedstocks 4 14 (78) (16) (11) (7) (19) (4) - - - (75) (41) Americas Styrenics 22 39 23 18 18 13 19 13 6 16 4 102 62 Corporate (27) (21) (24) (16) (26) (17) (17) (27) (26) (23) (20) (88) (87) Adjusted EBITDA** 178 164 (37) 6 36 57 41 20 45 67 66 312 154 Adj EBITDA Variance Analysis Net Timing** Impacts - Fav/(Unfav) Engineered Materials (0) 0 (1) (3) (7) (9) (6) 5 (7) 2 1 (3) (17) Latex Binders 3 (3) 7 (1) (0) (0) (2) 1 2 (1) 1 6 (1) Plastics Solutions 11 10 (1) (2) (2) (1) (1) 2 9 (7) 0 17 (2) Polystyrene 5 7 (6) (4) 1 (2) 2 (3) 9 (4) 1 1 (1) Feedstocks 13 19 (23) (8) 6 (4) 4 (4) - - - 1 1 Net Timing*** Impacts - Fav/(Unfav) 32 33 (24) (19) (2) (16) (4) 1 13 (10) 3 21 (20) *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. Segment Information – Excluding Feedstocks Recast

15 (in $millions, unless noted) Q1'22 Q2'22 Q3'22 Q4'22 Q1'23 Q2'23 Q3'23 Q4'23 Q1'24 Q2'24 Q3'24 2022 2023 Net Income (Loss) 16.7 37.4 (119.8) (365.3) (48.9) (349.0) (38.4) (265.0) (75.5) (67.8) (87.3) (430.9) (701.3) Net Income (Loss) from discontinued operations (0.4) 0.3 (1.9) (1.0) - - - - - - - (2.9) 0.0 Net Income (Loss) from continuing operations 17.1 37.1 (117.9) (364.3) (48.9) (349.0) (38.4) (265.0) (75.5) (67.8) (87.3) (428.0) (701.3) Interest expense, net 21.9 25.4 30.4 35.3 38.3 40.2 46.6 63.3 63.0 64.7 72.3 112.9 188.4 Provision for (benefit from) income taxes 22.6 30.8 (12.1) (83.0) (16.7) (25.1) (17.7) 127.9 5.4 20.3 3.4 (41.6) 68.4 Depreciation and amortization 53.0 48.1 45.9 89.8 56.0 52.5 38.2 74.4 45.0 46.6 48.3 236.9 221.2 EBITDA 114.6 141.4 (53.7) (322.2) 28.7 (281.4) 28.7 0.6 37.9 63.8 36.7 (119.8) (223.3) Other items 23.4 22.1 14.8 11.0 3.6 2.6 7.2 8.0 1.3 2.5 0.9 71.2 21.4 Restructuring and other charges 0.4 (1.5) - 17.0 3.7 1.5 13.8 12.5 9.4 4.0 28.5 15.9 31.5 Net gain on disposition of businesses and assets (0.3) (1.5) - - - (16.3) (9.3) 0.0 (3.6) (3.5) - (1.8) (25.6) Acquisition transaction and integration net costs 3.2 2.7 0.4 0.4 - 0.1 - (1.5) - - - 6.6 (1.4) Acquisition purchase price hedge loss (gain) - - - - - - - - - - - - - European Commission request for information 35.6 - - 0.6 - - - - - - - 36.2 - Goodwill impairment charges - - - 297.1 - 349.0 - - - - - 297.1 349.0 Asset impairment charges or write-offs 0.7 1.3 1.9 2.4 0.3 1.3 0.5 0.6 - - - 6.3 2.7 Adjusted EBITDA 177.6 164.5 (36.6) 6.3 36.3 56.8 40.9 20.2 45.0 66.8 66.1 311.7 154.3 Adjusted EBITDA to Adjusted Net Income Adjusted EBITDA 177.6 164.5 (36.6) 6.3 36.3 56.8 40.9 20.2 45.0 66.8 66.1 311.7 154.3 Interest expense, net 21.9 25.4 30.4 35.3 38.3 40.2 46.6 63.3 63.0 64.7 72.3 112.9 188.4 Provision for (benefit from) income taxes - Adjusted 25.6 25.7 (9.6) (18.8) (20.0) 34.8 (18.6) 12.1 4.2 5.9 3.5 22.8 8.3 Depreciation and amortization - Adjusted 50.9 47.2 45.1 49.9 53.3 49.5 49.2 50.0 46.3 47.9 47.8 193.1 202.0 Adjusted Net Income (Loss) 79.3 66.2 (102.5) (60.1) (35.3) (67.7) (36.3) (105.2) (68.5) (51.7) (57.5) (17.1) (244.4) Wtd Avg Shares - Diluted (000) 38,139 36,996 35,176 34,974 35,032 35,153 35,191 35,200 35,250 35,307 35,360 35,941 35,274 Adjusted EPS - Diluted ($) 2.08 1.79 (2.91) (1.72) (1.01) (1.92) (1.03) (2.99) (1.94) (1.46) (1.62) (0.48) (6.93) Adjustments by Statement of Operations Caption Loss on extinguishment of long-term debt - - - - - - - - - - 0.6 0.0 0.0 Cost of sales - - - - - 1.2 0.4 5.5 - - - 0.0 7.1 SG&A 27.0 22.9 16.0 28.4 7.3 (12.1) 15.4 13.5 7.1 6.5 29.6 94.3 24.1 Impairment and other charges 36.3 1.3 1.9 300.1 0.3 349.1 - 0.6 - - - 339.6 350.0 Acquisition purchase price hedge (gain) loss - - - - - - - - - - - 0.0 0.0 Other expense (income), net (0.3) (1.1) (0.8) - - - (3.6) - - (3.5) (0.8) (2.2) (3.6) Total EBITDA Adjustments 63.0 23.1 17.1 328.5 7.6 338.2 12.2 19.6 7.1 3.0 29.4 431.7 377.6 Free Cash Flow Reconciliation Cash provided by (used in) operating activities (5.0) (83.0) 97.6 33.9 45.4 56.5 29.3 17.5 (66.2) (41.9) 8.8 43.5 148.7 Capital expenditures (24.8) (31.5) (38.5) (54.2) (21.8) (13.8) (13.5) (20.6) (15.7) (14.2) (12.2) (149.0) (69.7) Free Cash Flow (29.8) (114.5) 59.1 (20.3) 23.6 42.7 15.8 (3.1) (81.9) (56.1) (3.4) (105.5) 79.0 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 to Adjusted EBITDA and to Adjusted Net Income, refer to the accompanying press release furnished as Exhibit 99.1 to our Form 8-K dated November 6, 2024. Totals may not sum due to rounding.

16 Quarter Ended Year Ended (In $millions, unless noted) Dec 31, 2024 Dec 31, 2024 Adjusted EBITDA 40 - 50 218 - 228 Interest expense, net 68 268 Provision for income taxes 5 34 Depreciation and amortization 48 188 Reconciling items to Adjusted EBITDA(1) 0 40 Net Income (loss) (81) - (71) (312) - (302) Reconciling items to Adjusted Net Income (Loss) (1) 0 (53) Adjusted Net Income (Loss) (81) - (71) (259) - (249) Weighted avg shares - diluted (MM) 35.3 35.3 EPS - diluted ($) (2.29) - (2.01) (8.82) - (8.54) Adjusted EPS ($) (2.29) - (2.01) (7.31) - (7.03) Quarter Ended Year Ended Dec 31, 2024 Dec 31, 2024 Cash from Operations 83 (15) Capital Expenditures (23) (65) Free Cash Flow 60 (80) US GAAP to Non-GAAP Reconciliation Profitability Outlook (1) Reconciling items to Adjusted EBITDA and Adjusted Net Income (Loss) are not typically forecasted by the Company based on their nature as being primarily driven by transactions that are not part of the core operations of the business and, as a result, cannot be estimated without unreasonable cost or uncertainty. For potential reconciling items to Adjusted EBITDA and Adjusted Net Income (Loss) during 2024 are not reflected. 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, 2024. Totals may not sum due to rounding. Cash Outlook