4. INTANGIBLES

Intangible assets consist of the following:


	Dollars in Thousands
	December 31, 2020
			Accumulated		Impairment		Net Book
	Cost		Amortization		Charge		Value
Technology	$	18,990	$	3,323	$	—	$	15,667
Customer relationships		250		250		—		—
Backlog		200		200		—		—
Covenants not to compete		30		30		—		—
Trademark		40		40		—		—
	$	19,510	$	3,843	$	—	$	15,667


	Dollars in Thousands
	December 31, 2019
			Accumulated		Impairment		Net Book
	Cost		Amortization		Charge		Value
Technology	$	18,990	$	2,374	$	—	$	16,616
Customer relationships		250		208		—		42
Backlog		200		200		—		—
Covenants not to compete		30		30		—		—
Trademark		40		40		—		—
IPR&D		1,590		—		1,590		—
	$	21,100	$	2,852	$	1,590	$	16,658


	Estimated Useful Life
Technology	20	years
Customer relationships	3	years
Backlog	1	year
Covenants not to compete	1	year
Trademark	2	years

Our IPR&D projects were accounted for as indefinite-lived intangible assets and subject to impairment testing. During 2019, the Company reviewed its IPR&D for impairment and determined that it was more likely than not that the IPR&D was fully impaired, resulting in an impairment charge of $1.6 million in 2019. For the year ended December 31, 2020, there was no impairment of IPR&D.

Amortization expense for intangible assets was $1.0 million during the years ended December 31, 2020 and 2019. Amortization expense for intangible assets is expected to be $0.9 million for each of the years ending December 31, 2021, 2022, 2023, 2024 and 2025, respectively.