7. Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):

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Depreciation and amortization expense related to property and equipment was $0.8 million and $0.3 million for the three months ended September 30, 2021 and 2020, and $1.9 million and $0.7 million for the nine months ended September 30, 2021, and 2020, respectively.

Leased equipment and the related accumulated depreciation were as follows:

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Depreciation related to leased units was $0.8 million and $0.2 million during the three months ended September 30, 2021 and 2020, respectively. Depreciation expense related to leased units was $1.8 million and $0.6 million during the nine months ended September 30, 2021 and 2020, respectively. Depreciable lives are generally 7 years, consistent with the Company’s planned and historical usage of the equipment subject to operating leases.

Impairment of property and equipment was $1.7 million for the three and nine months ended September 30, 2021. There was no impairment for the three and nine months ended September 30, 2020. This related to Edge units and prototype versions of Express that were removed from service and retired. The Company is transitioning domestic customers to Express which decreased the economic value of these assets and resulted in impairment.