PKG Packaging Corp

Notes to Financial Statements

December 31, 2015 and 2014

1. Description of the Plan

The following description of the Packaging Corporation of America Retirement Savings Plan for Salaried Employees (the “Plan”) provides general information. The Plan Sponsor is Packaging Corporation of America (the “Company” or PCA”). Participants should refer to the plan document for a more complete description of the Plan’s provisions.

General

The Plan is a defined-contribution plan, established on February 1, 2000, and is subject to the provisions of the Employee Retirement Income Security Act of 1974, as amended (“ERISA”). The Plan covers salaried employees of the Company and each of its domestic subsidiaries that have adopted the Plan who have completed six months of service, as defined. The Benefits Administration Committee is responsible for the oversight of the Plan. The Investment Committee determines the appropriateness of the Plan’s investment offerings and monitors investment performance. Both committees are appointed by the Board of Directors.

On October 25, 2013, PCA acquired 100% of the outstanding stock and voting equity interests of Boise, Inc. (“Boise”). As part of the integration of Boise into PCA, the assets of the Boise Paper Holdings L.L.C. Savings Plan and the Boise Paper Holdings L.L.C. Retirement Savings Plan (the “Boise Plans”) were transferred to the Packaging Corporation of America Defined Contribution Master Trust (the “Master Trust”) on October 1, 2015.

In connection with the integration efforts, the Company made a number of changes to the Plan, effective September 8, 2015, which included the following new features:

On October 1, 2014 certain employees at acquired container plants in City of Industry and San Bernardino, California became eligible for the Plan.

Aon Hewitt is the Plan’s record keeper. The Northern Trust is the Plan’s trustee and custodian. The Pavilion Advisory Group is the investment advisor to the Plan.

Contributions

Upon hire, participants may contribute between 1% and 50% of annual pretax compensation, as defined, with such contributions limited to $18,000 and $17,500 in 2015 and 2014, respectively for employees under age 50 and $24,000 and $23,000 in 2015 and 2014, respectively, for employees age 50 and older. Participants may also roll over qualifying distributions from other qualified plans.

The Company matches participant pretax contributions on the following basis:

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In addition to the Company’s matching contribution, the Company also makes a retirement savings contribution to eligible employees after six months of service up to 5% of compensation based on years of service, as defined. The contribution is made on behalf of the employee regardless of whether or not the employee is contributing to the Plan.

Beginning September 8, 2015, participants may now elect to make Roth contributions to the Plan, which are after-tax contributions whose earnings are not taxable upon qualified distribution. Total 2015 employee contributions, both before-tax and after-tax, cannot exceed $18,000 for employees under age 50 and $24,000 for employees age 50 and older.

Participant Accounts

Each participant’s account is credited with the participant’s contributions, Company contributions, and an allocation of Plan earnings (losses) and is charged with an allocation of administrative expenses. Allocations are based on each participant’s account balance, as defined, in relation to the balance of all participants’ account balances. The benefit to which a participant is entitled is the benefit that can be provided from the participant’s account.

Vesting

Participants are 100% vested immediately in the value of their pretax and Company matching contributions, earnings thereon and rollovers from other qualified plans.

The Company retirement savings contribution becomes 100% vested upon completion of three years of service, or upon reaching 65 years of age, permanent disability, or death while employed by the Company. Forfeited balances of non-vested terminated participants are applied to reduce future Company contributions.

Investment Options

Participants may elect to invest their ongoing pretax contributions, the Company retirement savings contribution, and the value of their entire accumulated account balance in any of the available investment options provided by the Plan. All matching contributions are invested in the PCA Common Stock Fund. Participants are eligible to transfer or withdraw the value from the PCA Common Stock Fund immediately following the deposit into their account.

Participants may change their investment options on any business day, subject to certain short-term trading restrictions outlined in the plan document.

The portion of the Plan currently invested in the PCA Common Stock Fund, and any future employee or employer contributions used to acquire PCA common stock, is invested in an Employee Stock Ownership Plan (“ESOP”). Plan participants have the ability to instruct the Plan’s trustee to distribute directly to them future cash dividends paid on shares of PCA common stock credited to their PCA common stock ESOP. The election to receive cash dividends is made through the PCA Benefits Center, and dividends will be reported as taxable income.

Benefit Payments

In the event of retirement (as defined in the Plan), death, permanent disability, or termination of employment, the vested balance in the participant’s account will be distributed to the participant or the participant’s beneficiary in a single lump-sum cash payment. The portion of the participant’s account invested in the PCA Common Stock Fund will be distributed in cash unless an election is made to be distributed in kind. In-service withdrawals of rollover contributions and related earnings and certain predecessor plan account balances, as defined, are available for any reason. Participants age 55 or older may withdraw the entire value, or any portion thereof, of their Company matching contributions and the vested value of their Company retirement savings contribution at any time. Participants who have attained the age of 59 1/2 may withdraw the entire value, or any portion thereof, of their account balance at any time.

Administrative Expenses

Administrative expenses are paid from Plan assets, to the extent not paid by the Company.

Notes Receivable from Participants

A participant may borrow an amount up to the lesser of $50,000 or 50% of their vested account balance. The minimum loan amount is $1,000. Such loans bear interest at the prime rate as published by The Wall Street Journal and are secured by

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the participant’s account balance in the Plan. Loans must be repaid within 54 months, with principal and interest payments made primarily through payroll deductions. Employees on unpaid leave may continue to repay loans via personal check or money order during their period of absence. Participants also have the ability to elect to make a one-time prepayment of their outstanding loan balance, of which the payment can be made via personal check or money order.

Effective September 8, 2015, participants may take up to two general purpose loans that must be repaid within 60 months.

Interest rates on loans outstanding in the Plan at December 31, 2015 ranged from 3.25% to 7.75%.

Forfeited Accounts

At December 31, 2015, forfeited non-vested accounts totaled $150,909. These accounts will be used to reduce future employer contributions. In 2015, employer contributions were reduced by $137,294 for forfeited non-vested accounts.

Plan Termination

Although it has not expressed any intent to do so, the Company has the right under the Plan to discontinue its contributions at any time and to terminate the Plan subject to the provisions of ERISA. In the event of Plan termination, participants will become 100% vested in the Company Contributions.

2. Significant Accounting Policies

Basis of Accounting

The financial statements have been prepared on the accrual basis of accounting.

Investment Valuation and Income Recognition

The Plan’s beneficial interest in the Master Trust represents the Plan’s share of the Master Trust’s investments stated at fair value. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (an exit price). See Note 4 for further discussion and disclosures related to fair value measurements.

Purchases and sales of securities are recorded on the settlement date. Interest income is recorded on the accrual basis. Dividends are recorded on the ex-dividend date. Net appreciation includes the gains and losses on investments bought and sold as well as held during the year.

Use of Estimates

The preparation of financial statements in conformity with principles generally accepted in the United States of America requires the Plan Administrator to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates.

Notes Receivable from Participants

Notes receivable from participants represent participant loans that are recorded at their unpaid principal balance plus any accrued but unpaid interest. Interest income on notes receivable from participants is recorded when it is earned. Related fees are recorded as administrative expenses and are expensed when they are incurred. No allowance for credit losses has been recorded as of December 31, 2015 or 2014. If a participant ceases to make loan repayments and the Plan Administrator deems the participant loan to be a distribution, the participant loan balance is reduced and a benefit payment is recorded.

Recently Issued or Newly Adopted Accounting Standards

In July 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2015-12, Plan Accounting: Defined Benefit Pension Plans (Topic 960), Defined Contribution Pension Plans (Topic 962), Health and Welfare Benefit Plans (Topic 965): (Part I) Fully Benefit-Responsive Investment Contracts, (Part II) Plan Investment Disclosures, (Part III) Measurement Date Practical Expedient . Part I of the ASU eliminates the requirements to measure fair value of fully benefit-responsive investment contracts and provide certain disclosures. Part II of the ASU eliminates the requirements to disclose individual investments that represent 5 percent or more of net assets available for benefits. It also simplifies the level of disaggregation of

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investments that are measured using fair value. Plans will continue to disaggregate investments that are measured using fair value by general type; however, plans are no longer required to also disaggregate investments by nature, characteristics, and risks. Further, the disclosure of information about fair value measurements shall be provided by general type of plan asset. Part III of the ASU allows a plan with a fiscal year end that does not coincide with the end of a calendar month to measure its investments and investment-related accounts using the month end closest to its fiscal year end. The ASU is effective for fiscal years beginning after December 15, 2015. Parts I and II are to be applied retrospectively. Part III is to be applied prospectively. Plans can early adopt any of the ASU’s three parts without early adopting the other parts. Management has elected to adopt Parts I and II of the ASU early. Part III is not applicable to the Plan. The adoption was applied retrospectively and resulted in the elimination of the disclosures noted above. The adoption of this accounting guidance did not have an effect on the Plan’s net assets available for benefits or changes in net assets available for benefits. See Note 3, Master Trust, for the new simplified disclosures related to the Plan’s investments.

In May 2015, the FASB issued ASU 2015-07, Fair Value Measurement (Topic 820): Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent) . This ASU removes the requirement to categorize within the fair value hierarchy all investments for which fair value is measured using the net asset value per share practical expedient. This ASU also removes the requirement to make certain disclosures for all investments that are eligible to be measured at fair value using the net asset value per share practical expedient. Rather, those disclosures are limited to investments for which the entity has elected to measure the fair value using that practical expedient. Although the new standard is not effective until annual and interim reporting periods beginning after December 15, 2016, early adoption is permitted. The Plan early adopted the provisions of this guidance effective January 1, 2015, and the adoption had no impact on the Plan’s financial statements. See Note 4, Fair Value Measurements, for the new fair value disclosures related to the Plan’s investments.

There were no other accounting standards recently issued that had or are expected to have a material impact on the Plan’s financial statements and associated disclosures.

3. Master Trust

On October 1, 2015, assets of the Boise Plans were transferred into the Master Trust. At December 31. 2015, the Master Trust includes assets of the Plan, the Packaging Corporation of America Thrift Plan for Hourly Employees, the Boise Paper Holdings L.L.C Savings Plan and the Boise Paper Holdings L.L.C. Retirement Savings Plan. All of the Plan’s investments are invested in the Master Trust. The purpose of the Master Trust is the collective investment of assets of participating plans. Each participating plan’s interest in the Master Trust is based on the aggregate account balances of the participants in the respective participating plan. The Master Trust specifically identifies contributions, benefit payments, and plan-specific expenses attributable to each participating plan. Investment gains (losses) are allocated to each participating plan in the Master Trust on a daily basis based on each plan’s separate interest in the Master Trust. At December 31, 2015 and 2014, the Plan’s interest in the net assets of the Master Trust at fair value was 37.7% and 69.0%, or $472,311,328 or $489,066,771, respectively.

The investments held by the Master Trust and the Plan’s percentage interest in each of the investments within the Master Trust are presented below.

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Investment income for the Master Trust was as follows:

4. Fair Value Measurements

Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (i.e., an exit price). The fair value hierarchy prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets and liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). The three levels of the fair value hierarchy are described below:

Level 1 — Unadjusted quoted prices in active markets that are accessible to the reporting entity at the measurement date for identical assets and liabilities.

Level 2 — Inputs other than quoted prices in active markets for identical assets and liabilities that are observable either directly or indirectly for substantially the full term of the asset or liability. Level 2 inputs include the following:

Level 3 — Unobservable inputs for the asset or liability (i.e., supported by little or no market activity). Level 3 inputs include management’s own assumption about the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk).

The level in the fair value hierarchy within which the fair value measurement is classified is determined based on the lowest level of input that is significant to the fair value measurement in its entirety.

The following is a description of the valuation techniques and inputs used for each major class of assets measured at fair value by the Plan.

Mutual funds: Valued at the daily closing price reported by the funds. Mutual funds held by the Plan are open-ended mutual funds that are registered with the Securities Exchange Commission. These funds are required to publish daily net asset values (“NAV”) and to transact at that price. The mutual funds held by the Plan are considered actively traded.

Common stocks: Valued at its year-end unit closing price (comprised of year-end market price plus uninvested cash position).

Self-directed brokerage account: Valued at the closing price reported on the active market on which the individual securities are traded.

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Target date funds: Valued at the NAV provided by the Trustee. While the underlying assets are actively traded on an exchange, the funds are not.

Common collective trust funds: Valued at the NAV provided by the administrator of the fund which is used as a practical expedient to estimate fair value. The NAV is based on the underlying assets owned by the fund, minus its liabilities, and then divided by the number of shares outstanding. The Plan has no contractual obligations to further invest in the funds.

Short-term investments: Valued at cost, which approximates fair value.

The following tables set forth by level, within the fair value hierarchy, the Master Trust’s assets carried at fair value: The table as of December 31, 2014, has been revised to reflect the adopted provision of ASU 2015-07 discussed in Note 2, Significant Accounting Policies.

There were no significant transfers between levels 1, 2 or 3.

5. Tax Status

The Plan has received a determination letter from the Internal Revenue Service (“IRS”) dated October 14, 2014 stating that the Plan is qualified under Section 401(a) of the Internal Revenue Code (“the Code”) and therefore, the related trust is exempt from taxation. Subsequent to this determination by the IRS, the Plan was amended. Once qualified, the Plan is required to operate in conformity with the Code to maintain its qualified status. The Plan administrator believes the Plan is being operated in compliance with the applicable requirements of the Code and, therefore, believes the Plan, as amended, is qualified and the related trust is tax-exempt.

Accounting principles generally accepted in the United States require plan management to evaluate uncertain tax positions taken by the Plan. The financial statement effects of a tax position are recognized when the position is more likely than not, based on the technical merits, to be sustained upon examination by the IRS. The Plan Administrator has analyzed the tax positions taken by the Plan and has concluded that as of December 31, 2015, there are no uncertain positions taken or expected to be taken. The Plan has recognized no interest or penalties related to uncertain tax positions. The Plan is subject to routine audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress. The Plan Administrator believes it is no longer subject to federal income tax examinations for years prior to 2012.

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6. Risks and Uncertainties

The Plan invests in various investment securities. Investment securities are exposed to various risks such as interest rate, market, and credit risks. Due to the level of risk associated with certain investment securities, it is at least reasonably possible that changes in the values of investment securities will occur in the near term and that such changes could materially affect participants’ account balances and the amounts reported in the statements of net assets available for benefits.

7. Reconciliation of Financial Statements to Form 5500

The following is a reconciliation of net assets available for benefits per the financial statements to Form 5500:

The following is a reconciliation of net decrease per the financial statements to Form 5500:

8. Related Party Transactions

The Master Trust invests in the common stock of the Company. These transactions qualify as party-in-interest transactions; however, they are exempt from the prohibited transactions rules under ERISA. During 2015, the Plan received $4,871,159 in common stock dividends from the Company.

The Plan’s record keeper, trustee, custodian and investment advisor described in Note 1 are each a party-in-interest to the Plan as defined by ERISA. Parties in interest to the Plan are noted in the Schedule H, Line 4i—Schedule of Assets. KPMG LLP, the auditor of the Plan’s financial statements, is also a party in interest.

9. Subsequent Events

Effective January 1, 2016, Company matching contributions will be invested in the same investment options the participants have elected for their pretax contributions instead of invested in the PCA Common Stock Fund.

The Company has evaluated subsequent events after the Statement of Net Assets Available for Plan Benefits date through June 28, 2016, the date that the financial statements were issued.

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Supplemental Schedule

Packaging Corporation of America

Retirement Savings Plan for Salaried Employees

Schedule H, Line 4i—Schedule of Assets

(Held at End of Year)