On a consolidated basis, the company reported net sales for the fourth quarter of $453 million and adjusted EBITDA of $72 million.
Which represents growth of approximately 4% and 38%, respectively, over the fourth quarter of last year.
Our backlogs are robust, which contributed to our decision to announce a price increase of $50 per ton across our SBS portfolio, starting on February 2.
In the fourth quarter, we used the free cash flows generated to reduce net debt by an additional $58 million.
As a recognition of the work by our entire team during this challenging time, we paid out a onetime discretionary bonus of $1,000 in November to over 2,800 of our people.
We're also strongly encouraging all our people to get the COVID vaccine with a $200 incentive.
First, recall that the market for tissue in the U.S. is traditionally 2/3 at-home and 1/3 away-from-home, with limited manufacturing production capability to swing between the 2.
We shipped 13.9 million cases, which was up around 5.3% compared to the fourth quarter of 2019.
Sales were down 4.2% relative to the third quarter of 2020.
As you recall, we estimate that approximately 2/3 of paperboard demand is derived from products that are more recession-resilient and 1/3 is driven by economically -- by more economically sensitive or discretionary products.
We estimate that the costs associated with the weather event across our paperboard system, including loss production, repairs and spikes in natural gas prices, could impact us in the first quarter by approximately $6 million to $8 million.
We continue to experience the same fundamental supply and demand dynamics that led us to announce a $50 per ton price increase in January.
In the fourth quarter, diluted net income per share was $1.34 per share and adjusted EBITDA was $71.6 million and full year diluted net income per share was $4.61 per share, and adjusted EBITDA was $283.2 million.
Our sales in the fourth quarter were 13.9 million cases, representing a unit decline of 4.2% versus the third quarter and unit growth of 5.3% versus prior year.
Our production in the quarter was $13.9 million cases or down 9% versus the third quarter and up 2.4% versus prior year.
Tissue shipments in January were 4.6 million cases, and our shipments in February are trending to below four million cases.
As we mentioned previously, our paperboard business announced a price increase of $50 a ton across our SBS grades effective February 2.
The unexpected weather-related outage at our Arkansas mill, which caused loss production and repairs as well as natural gas price increases across our paperboard system, is expected to negatively impact the quarter by approximately $6 million to $8 million.
If our assumptions are correct, we would anticipate the first quarter adjusted EBITDA to be in the range of $51 million to $59 million.
While these variables are difficult to predict today, raw material inputs in total could be a $40 million to $50 million headwind this year, with more than half the total coming from pulp.
In our paperboard business, planned major maintenance outages are expected to reduce our earnings for 2021 compared to 2020 by $25 million to $30 million.
For the full year 2021, we're also anticipating the following: interest expense between $38 million and $40 million.
Depreciation is expected to be between $106 million and $110 million.
Capital expenditures are expected to be between $60 million and $65 million, which is closer to historical trends as we expect to execute against some projects that were delayed in 2020.
And our effective tax rate is expected to be 25% to 26%, and we expect to utilize some of our current tax attributes which amount to $60 million to reduce cash taxes.
We utilized approximately $50 million of free cash flow to reduce our net debt, including making voluntary prepayments on our term loan, and our liquidity was $250 million at the end of the year.
We continue to make strides in reducing our net debt and increasing our financial flexibility as we target a net debt to adjusted EBITDA ratio of 2.5 times, assuming adjusted EBITDA after COVID benefits and with a normal amount of outages.
We delivered outstanding financial results, reduced net debt by $200 million, refinanced our near-term debt maturities and strengthen our balance sheet.
Private brand tissue share in the U.S. rose to over 30% in 2019, up from 18% in 2011.
As we demonstrated in the fourth quarter, with a net debt reduction of approximately $58 million, bringing our net reduction in 2020 to over $200 million.
With an adjusted EBITDA impacted by normal outages and reduced COVID benefits, we do not anticipate achieving our 2.5 leverage target this year.

Summary:
On a consolidated basis, the company reported net sales for the fourth quarter of $453 million and adjusted EBITDA of $72 million.
In the fourth quarter, diluted net income per share was $1.34 per share and adjusted EBITDA was $71.6 million and full year diluted net income per share was $4.61 per share, and adjusted EBITDA was $283.2 million.