Since the onset of the pandemic, we have expanded capacity at 13 existing sites with 30 major facility modifications, dedicated over $300 million of capital, and added over 400 incremental pieces of equipment, all while keeping pace with a growing base demand and moving our operations to 24/7.
Our financial results are summarized on Slide 9 and the reconciliation of non-U.S. GAAP measures are described on Slides 17 to 21.
We recorded net sales of $706.5 million, representing organic sales growth of 27.9%.
And COVID-related net revenues are estimated to have been approximately $115 million in the quarter.
Proprietary Products sales grew organically by 35.7% in the quarter.
High-value products, which made up approximately 73% of proprietary product sales in the quarter grew double digits and had solid momentum across all of our market units in Q3.
We recorded $288.2 million in gross profit, 93.6 million or 48.1% above Q3 of last year.
And our gross profit margin of 14.8% was a 530 basis point expansion from the same period last year.
We saw improvement in adjusted operating profit with $182.8 million recorded this quarter, compared to 103.9 million in the same period last year for a 75.9% increase.
Our adjusted operating profit margin, 25.9%, was a 690 basis point increase from the same period last year.
Finally, adjusted diluted earnings per share grew 79% for Q3.
Excluding stock-based compensation tax benefit of $0.11 in Q3, earnings per share grew by approximately 72%.
Volume and mix contributed $142.9 million or 26.1 percentage points of growth, including approximately 83 million of incremental volume driven by COVID-19-related net demand.
Sales price increases contributed 10.1 million or 1.8 percentage points of growth.
Slide 19 shows our consolidated gross profit margin of 40.8% for Q3 2021, up 35.5% in Q3 2020.
Proprietary products third quarter gross profit margin of 46.3% was 550 basis points above the margin achieved in the third quarter of 2020.
Contract manufacturing third quarter gross profit margin of 16.1% was 180 basis points below the margin achieved in the quarter of 2020.
Operating cash flow was $423.2 million for the third quarter of 2021, an increase of 99.4 million compared to the same period last year, a 30.7% increase.
Our third quarter 2021 year-to-date capital spending was $176.9 million, $60.2 million higher than the same period last year.
Working capital of approximately $1 billion at September 30th, 2021 increased by 169.4 million from December 31, 2020, primarily due to higher accounts receivable from our increased sales.
Our cash balance at September 30th of $688 million was $72.5 million higher than our December 2020 balance.
Full year 2021 net sales are expected to be in a range of 2.8 billion and $2.81 billion, compared to our prior guidance range of 2.76 billion to $2.785 billion.
This guidance includes estimated net coal with incremental revenues of approximately $450 million.
There is an estimated benefit of $55 million based on current foreign exchange rates, compared to a prior estimated benefit of $80 million.
This $25 million reduction in FX tailwind has been absorbed into our guidance.
We expect organic sales growth to be approximately 28%, compared to a prior range of 24 to 25%.
We expect our full year 2021 reported diluted earnings per share guidance to be in a range of $8.40 to $8.50, compared to a prior range of $8.05 to $8.20.
This revised guidance includes a $0.35 earnings per share positive impact of tax benefits from stock-based compensation from the first nine months 2021.
Also, our capex guidance remains at 265 to $275 million for the year.
Estimated FX benefit on earnings per share has an impact of approximately $0.19 based on current foreign currency exchange rates compared to a prior estimated benefit of $0.27.

Summary:
We recorded net sales of $706.5 million, representing organic sales growth of 27.9%.
Full year 2021 net sales are expected to be in a range of 2.8 billion and $2.81 billion, compared to our prior guidance range of 2.76 billion to $2.785 billion.
We expect our full year 2021 reported diluted earnings per share guidance to be in a range of $8.40 to $8.50, compared to a prior range of $8.05 to $8.20.