v3.26.1
Intangible assets (Details) - EUR (€)
€ in Thousands
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Reconciliation of changes in intangible assets other than goodwill [abstract]    
Intangible assets at beginning of period € 7 € 8
Increases 3  
Decreases 0 0
Transfer 0 0
Currency translation 0 0
Intangible assets at end of period 10 7
Gross book value of intangible assets | Patents    
Reconciliation of changes in intangible assets other than goodwill [abstract]    
Intangible assets at beginning of period 65 65
Increases 7 0
Decreases 0 0
Transfer 0 0
Currency translation 0 0
Intangible assets at end of period 72 65
Gross book value of intangible assets | Software    
Reconciliation of changes in intangible assets other than goodwill [abstract]    
Intangible assets at beginning of period 669 667
Increases 1 2
Decreases 0 0
Transfer 0 0
Currency translation 0 0
Intangible assets at end of period 669 669
Gross book value of intangible assets    
Reconciliation of changes in intangible assets other than goodwill [abstract]    
Intangible assets at beginning of period 734 732
Increases 8 2
Decreases 0 0
Transfer 0 0
Currency translation 0 0
Intangible assets at end of period 742 734
Accumulated depreciation of intangible assets | Patents    
Reconciliation of changes in intangible assets other than goodwill [abstract]    
Intangible assets at beginning of period (65) (65)
Increases (1) 0
Decreases 0 0
Transfer 0 0
Currency translation 0 0
Intangible assets at end of period (66) (65)
Accumulated depreciation of intangible assets | Software    
Reconciliation of changes in intangible assets other than goodwill [abstract]    
Intangible assets at beginning of period (662) (659)
Increases (4) (4)
Decreases 0 0
Transfer 0 0
Currency translation 0 0
Intangible assets at end of period (666) (662)
Accumulated depreciation of intangible assets    
Reconciliation of changes in intangible assets other than goodwill [abstract]    
Intangible assets at beginning of period (727) (724)
Increases (5) (4)
Decreases 0 0
Transfer 0 0
Currency translation 0 0
Intangible assets at end of period € (732) (727)
Netting    
Reconciliation of changes in intangible assets other than goodwill [abstract]    
Increases   € (2)