Power density has become a critical figure of merit in power conversion systems, especially in automotive and aerospace applications. Nowadays, wide band gap (WBG) devices are revolutionizing power conversion by enabling unprecedented levels of efficiency and power density. High power density is possible only with advanced integrated cooling solutions based on custom-made heatsinks that must be properly tailored to match the packages of the WBG devices selected for the application. However, the design and prototyping of custom-made heatsinks, typically crafted from aluminium, require significant cost and time during the converter iterative prototyping phases. To address these challenges, this digest proposes a liquid-cooled heatsink made of a combination of 3D printed plastic material and aluminum. The proposed heatsink, tailored for rapid prototyping, leads to a drastic reduction in costs and development time compared to traditional aluminum heatsinks. Moreover, the incorporation of plastic material delivers additional benefits, including reduced weight and seamless integration with electronic components, owing to its inherent insulating properties.