A cooler comprising an inlet, an outlet, a first unit, a second unit and a third unit, - the inlet configured for feeding the cooler with coolant, - the outlet configured for discharging said coolant, - the first unit comprising a first plane for receiving a first part to be cooled and a set of first unit fins forming cavities, - the third unit comprising a set of third unit fins forming cavities, - the second unit - embodied as insert - having a set of second unit fins inserted into the cavities formed by the sets of the first and the third unit fins, - the second unit fins each having a second unit fins first surface and a second unit fins second surface, - the insert having a both-sidedly corrugated structure, - the second unit fins abutting the first and the third unit fins forming inbound channels - between the second unit fins first surface and the first and the third unit fins - and forming reverse channels - between the second unit fins second surfaces and the first and the third unit fins - in such a way that ∘ the inbound channels being configured for ▪ forming coolant inbound flows towards roots of the first unit and the third unit and ▪ causing the coolant flows to impinge and laterally widen on the roots of the first unit and the third unit ∘ and that the reverse channels being configured for ▪ forming coolant back-flows after impinging on the respective roots. - the inlet configured for feeding the cooler with coolant, - the outlet configured for discharging said coolant, - the first unit comprising a first plane for receiving a first part to be cooled and a set of first unit fins forming cavities, - the third unit comprising a set of third unit fins forming cavities, - the second unit - embodied as insert - having a set of second unit fins inserted into the cavities formed by the sets of the first and the third unit fins, - the second unit fins each having a second unit fins first surface and a second unit fins second surface, - the insert having a both-sidedly corrugated structure, - the second unit fins abutting the first and the third unit fins forming inbound channels - between the second unit fins first surface and the first and the third unit fins - and forming reverse channels - between the second unit fins second surfaces and the first and the third unit fins - in such a way that ∘ the inbound channels being configured for ▪ forming coolant inbound flows towards roots of the first unit and the third unit and ▪ causing the coolant flows to impinge and laterally widen on the roots of the first unit and the third unit ∘ and that the reverse channels being configured for ▪ forming coolant back-flows after impinging on the respective roots. ∘ the inbound channels being configured for ▪ forming coolant inbound flows towards roots of the first unit and the third unit and ▪ causing the coolant flows to impinge and laterally widen on the roots of the first unit and the third unit ▪ forming coolant inbound flows towards roots of the first unit and the third unit and ▪ causing the coolant flows to impinge and laterally widen on the roots of the first unit and the third unit ∘ and that the reverse channels being configured for ▪ forming coolant back-flows after impinging on the respective roots. ▪ forming coolant back-flows after impinging on the respective roots.