Net sales for the three months ended September 30, 2021, increased by $5.5 million or 1.2% to $479.6 million as compared to $474.1 million in the same period in 2020. Net sales of wind blades increased by $0.6 million or 0.1% to $450.7 million for the three months ended September 30, 2021, as compared to $450.1 million in the same period in 2020.
Net sales were positively impacted by an increase in the average selling price due to the mix of wind blade models produced, offset by a 20% decrease in the number of wind blades produced primarily due to reductions in manufacturing lines under contract in China. The three months ended September 30, 2021 were also impacted by the transition to an innovative blade in Juarez, Mexico, the impact on its production due to shortages of raw material supplied by its customers, and a temporary shutdown of its Yangzhou manufacturing facility due to a COVID-19 outbreak in Yangzhou City.
Total cost of goods sold for the three months ended September 30, 2021, was $486.7 million and included $4.5 million of costs related to lines in startup and $10.0 million of costs related to lines in transition during the period. This compares to total cost of goods sold for the three months ended September 30, 2020, of $433.6 million and included $5.1 million of costs related to lines in startup and $3.4 million of costs related to lines in transition during the period. Total cost of goods sold as a percentage of net sales increased by approximately ten percentage points during the three months ended September 30, 2021, as compared to the same period in 2020, driven primarily by increases in direct material costs, direct labor costs and foreign currency fluctuations.
General and administrative expenses for the three months ended September 30, 2021, totaled $8.2 million, or 1.7% of net sales, compared to $9.3 million, or 2.0% of net sales, for the same period in 2020. Net loss for the three months ended September 30, 2021, was $30.7 million as compared to net income of $42.4 million in the same period in 2020.
Adjusted EBITDA for the three months ended September 30, 2021, decreased to $0.2 million as compared to $49.1 million during the same period in 2020. Adjusted EBITDA margin decreased to zero as compared to 10.4% during the same period in 2020.
