About Cocoon At Cocoon, we’re building low-carbon construction materials for the builders of tomorrow. Steel and cement together account for nearly 15% of global CO₂ emissions — and we’re tackling that challenge by developing a low-carbon cement substitute designed for industrial deployment. We’re an early-stage, fast-growing company with a small, hands-on team and a big mission. Following successful initial trials, we’re now accelerating development toward industrial scale. The Role We’re looking for a Mechanical Engineer to lead the design, build, and validation of mechanical systems and test rigs that underpin Cocoon’s next-generation slag activation technology. You’ll work closely with engineers, material scientists, researchers, and technicians to mature R&D outputs into robust, scalable system designs. This role spans experimental design, detailed mechanical engineering, supplier coordination, and hands-on testing in the UK and overseas. You’ll own end-to-end development and validation workstreams — from concept through commissioning — and play a key role in scaling our technology toward our first industrial plant. Responsibilities Mechanical Design & Development Lead mechanical engineering for R&D workstreams, owning delivery from concept to validation. Design experiments, methods, and associated test rigs to validate and advance core technologies. Develop mechanical designs for hydraulic systems, industrial instrumentation, and bulk material handling systems. Use simulation, first principles, and engineering judgement to validate designs. Build, Testing & Validation Source components and manage subcontractors for delivering designs and test rigs. Manage the build and delivery of test rigs; create assembly documentation and direct manufacturing and installation activities. Lead validation and testing activities in the UK and overseas, from requirements definition through commissioning and testing. Create documentation for validation and compliance activities (DFMEA, risk registers, operating instructions, test reports). Support testing campaigns at Cocoon’s London R&D facility, UK pilot facilities, and US partner sites. Scale-Up & Delivery Collaborate closely with the process engineering team to translate R&D outputs into system specifications for industrial deployment. Provide technical direction to engineers, technicians, and suppliers. Contribute to scaling technologies from R&D toward pilot and industrial deployment. Travel extensively during test campaigns to support installation, commissioning, and testing activities. You’ll Succeed In This Role If You… Hold a Master’s degree in engineering and have at least two years of industry experience in mechanical, hydraulic, or electromechanical systems. Have experience designing experiments, developing test rigs, and managing validation testing. Are comfortable owning complete development and validation workstreams in a fast-moving environment. Bring strong problem-solving skills and enjoy hands-on troubleshooting and prototype building. Communicate clearly with technical and non-technical stakeholders and can lead work delivered by others. Bonus qualities Knowledge of industrial automation, instrumentation, or PLCs. Understanding of process engineering (material handling, heat transfer, unit operations). Experience with high-temperature fluid handling or metallurgical systems. Experience scaling technologies from TRL 4/5 to TRL 8/9. Background in steelmaking or related heavy industrial environments. What We Offer A hands-on engineering role at the centre of Cocoon’s scale-up journey. Ownership of real hardware development and validation work. Close collaboration with a multidisciplinary, mission-driven team. Competitive salary and stock options. Apply Now If you’re excited about designing, building, and validating first-of-a-kind mechanical systems — and helping decarbonise heavy industry — we’d love to hear from you.