Property, plant and equipment, net, consisted of the following:


		June 30,			December 31,
(in thousands)	Estimated Useful Life (Years)	2024			2023
Land and improvements	20	$	92		$	92
Leasehold improvements	Shorter of useful life or lease term		110,543			110,531
Buildings	20-40		2,191			2,191
Machinery and equipment	3-20		190,254			190,111
Motor vehicles	7-10		903			903
Furniture and fixtures	3-10		474			474
Office equipment	3-10		7,434			7,415
Construction in progress	N/A		204,500			202,998
			516,391			514,715
Accumulated depreciation and amortization			(82,134	)		(69,562	)
Property, plant and equipment, net		$	434,257		$	445,153

We reported depreciation and amortization expense (which included amortization of intangible assets) as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2024		2023		2024		2023
Cost of revenue	$	5,105	$	4,934	$	10,252	$	10,147
Research and development		1,973		1,956		4,004		4,038
Selling, general and administrative		360		283		713		567
Total depreciation and amortization expense	$	7,438	$	7,173	$	14,969	$	14,752

Construction in progress consists primarily of the early phases of construction of our PHA plant in Bainbridge, Georgia (“Greenfield Facility”) as noted in the table below. We do not have expected in-service dates for our Greenfield Facility, since we have paused major construction. We will need to obtain additional financing to complete our Greenfield Facility. In 2022, the engineering cost estimate ranged from $515 million to $665 million, which does not consider any effect of subsequent inflation, and if we do not obtain financing, our investment could be impaired.


(in thousands)	June 30, 2024		December 31, 2023
Georgia	$	200,482	$	199,342
Kentucky		2,193		1,696
New York		1,825		1,960
	$	204,500	$	202,998

Property, plant and equipment includes gross capitalized interest of $15.0 million as of both June 30, 2024 and December 31, 2023. For the three and six months ended June 30, 2024 and 2023, capitalized interest costs were immaterial.