We finished a challenging year with a very strong fourth quarter realizing record high revenue of $388 million and double-digit improvements in free cash flow.
From a full-year perspective, our revenue declined 3%.
Despite the revenue challenges in certain areas, our annual adjusted operating margin reached 18%, that's up 10 basis points from a year ago.
We've talked about our long-term aspiration to get our operating margins into the 20% range over the coming years.
The accomplishments of our founders back in 1914 reflects what happens every day in MSA's product development labs around the world.
This electric lamp helped reduce mining fatalities by 75% over the next 25 years.
In 2020, we invested nearly $70 million in R&D to bring the most advanced safety solutions to our global customer base.
One example is our new Advantage 290 reusable respirator.
The Advantage 290 is the first government-approved reusable respirator designed without an exhalation valve.
As an example, our long-term goal was to improve operating margin in the International segment by 500 basis points over 2017.
In 2020, the International segment operating margin rose to 15%.
This is a 270-basis-point improvement compared to 2019 despite the 3% revenue decline.
And to-date, we've achieved 400 basis points of segment margin expansion.
Our fire service business increased 10% in the fourth quarter of 2020, even in the face of the pandemic.
Second, our profitability was strong as adjusted operating margin expanded by 10 basis points.
This equates to a 14% decremental operating margin.
We delivered on our goal to manage decremental margins at a lower rate than our incremental margins, improving overall operating margins to 18% on lower revenue volume is another step in the right direction for reaching our long-term margin aspirations.
And third, we generated more than $200 million of operating cash flow in 2020 or 25% higher than a year ago.
We invested $49 million in capex projects.
We paid down $44 million of debt.
We funded $67 million in dividends to our shareholders and deployed $20 million for share repurchases.
And just last month, we deployed approximately $60 million for the acquisition of Bristol Uniforms.
Our net leverage continues to track below 1 times as we enter 2021.
Quarterly revenue was a record high of $388 million, growing over 3% from a year ago or 2% in constant currency.
From a geographic perspective, revenue increased 5% in the Americas segment and decreased 2% in the International segment in constant currency.
Shifting gears to the employment-based industrial PPE products, which were down 4% year-over-year after declining by 25% in the third quarter.
Our FGFD business was down 7% in the quarter on tough comparisons in both the Americas and International segments.
For the full year, we had a 2% decline in FGFD, reflecting the support from that recurring revenue streams in the product line that we've discussed with you previously.
Revenues from air purifying respirator lines increased 32% from a year ago.
If you recall, our Q1 results a year ago included approximately $10 million of incremental revenue from APR at the onset of the pandemic.
Gross profit declined 350 basis points from a year ago as we incurred about $11 million of higher costs in the quarter.
$5 million of these costs were associated with lower throughput in certain factories and $6 million is primarily associated with inventory-related charges, which we don't expect to continue into 2021.
SG&A expense of $76 million was down 10% from a year ago.
We delivered $6 million to $8 million of savings from previously executed restructuring programs and discretionary cost savings in the quarter associated with reduced travel, controlled hiring, professional services and other costs, and $3 million of savings from variable compensation on a year-over-year basis.
We incurred $9 million of quarterly restructuring expense to accrue for cost reduction programs related to footprint rationalization and business model optimization, primarily in the International segment where operating margin is up 270 basis points for the year.
Together with the programs we've discussed throughout 2020, we expect to deliver approximately $15 million of savings across the income statement in 2021 and annual savings of $20 million thereafter.
Quarterly adjusted operating margin was flat with the prior year at 17.3% as the cost discipline and SG&A was offset by the gross profit headwinds.
International margins were up 320 basis points and were 17.5% in the quarter, which very much reflects the results the team are driving in pricing and cost reduction initiatives.
Americas' margins were down 260 basis points and were 20.8%.
The $11 million of higher cost in gross profit that I mentioned a moment ago was incurred primarily in the Americas segment.
From a cash flow and capital allocation perspective, quarterly free cash flow conversion was well north of 100%.
We saw strong performance across working capital, which declined 320 basis points as a percentage of sales.
As part of that review, we reflected changes in underlying assumptions in our model that increase our product liability reserve and resulted in a pre-tax charge of $34 million, net of insurance recoveries on the income statement.
For example, over the past five years, our average cash conversion has exceeded 100% of net income both with and without the impact of product liability and insurance receivables.
While we are in the midst of finalizing our purchase accounting for the acquisition, we expect earnings accretion in the first year of ownership, excluding acquisition-related amortization of about $0.03 to $0.05 per share.

Summary:
Quarterly revenue was a record high of $388 million, growing over 3% from a year ago or 2% in constant currency.