Net Sales
Net sales were $587.8 million for the three fiscal quarters ended October 1, 2022, compared to $491.6 million for three fiscal quarters ended October 2, 2021. The $96.2 million, or 19.6%, increase in net sales was due to a $97.4 million increase from pricing, partially offset by a $1.2 million decrease from volume. The $97.4 million price increase reflects the impact of pricing actions to address inflation. The increase in total net sales of $96.2 million across our product lines consisted of $40.6 million for in-ground swimming pools, $27.1 million for liners and $28.5 million for covers.
Cost of Sales and Gross Margin
Cost of sales was $390.7 million for the three fiscal quarters ended October 1, 2022, compared to $329.8 million for the three fiscal quarters ended October 2, 2021. Gross margin increased by 0.6%, to 33.5% of net sales for the three fiscal quarters ended October 1, 2022 compared to 32.9% of net sales for the three fiscal quarters ended October 2, 2021. The $60.9 million, or 18.5%, increase in cost of sales was primarily the result of cost inflation, partially offset by a $3.8 million decrease in non-cash stock-based compensation expense. The 0.6% increase in gross margin was primarily driven by lower non-cash stock-based compensation expense and benefits from the build of inventory, partially offset by pricing actions that offset inflation, although not at a magnitude to hold gross margins year-over-year.
Selling, General and Administrative Expense
Selling, general and administrative expense was $113.8 million for the three fiscal quarters ended October 1, 2022, compared to $170.5 million for the three fiscal quarters ended October 2, 2021, and decreased as a percentage of net sales by 15.3%. The $56.7 million, or 33.3%, decrease in selling, general and administrative expense was primarily due to a $60.4 million decrease in non-cash stock-based compensation expense, partially offset by a $1.2 million increase in ongoing public company costs, and an increase in insurance and travel related expenses.
Underwriting Fees Related to Offering of Common Stock
Underwriting fees related to our offering of common stock were $11.4 million for the three fiscal quarters ended October 1, 2022, related to the offering that was completed in January 2022.
Amortization
Amortization was $21.5 million for the three fiscal quarters ended October 1, 2022, compared to $16.6 million for the three fiscal quarters ended October 2, 2021. The $4.9 million, or 29.9%, increase in amortization was due to the increase in our definite-lived intangible assets resulting from our acquisition of Radiant in November 2021.
Interest Expense
Interest expense was $9.2 million for the three fiscal quarters ended October 1, 2022, compared to $20.8 million for the three fiscal quarters ended October 2, 2021. The $11.6 million, or 55.9%, decrease in interest expense was primarily due to lower amortization of deferred financing costs and debt discount and a lower effective interest rate due to the refinancing, compared to the three fiscal quarters ended October 2, 2021. In addition, interest expense for the three fiscal quarters ended October 1, 2022 was partially offset by an unrealized gain of $4.2 million related to the change in fair value of our interest rate swap.
Loss on Extinguishment of Debt
Loss on extinguishment of debt was $3.5 million for the three fiscal quarters ended October 1, 2022, compared to none for the three fiscal quarters ended October 2, 2021, as our debt refinancing was completed in February 2022.
Other Expense (Income), Net
Other expense (income), net was $1.6 million for the three fiscal quarters ended October 1, 2022, compared to ($3.9) million for the three fiscal quarters ended October 2, 2021. The $5.5 million increase in other expense was primarily due to a non-recurring $3.9