Water-assisted injection moulding. Compared with gas, water offers good thermal conductivity, high heat capacity, incompressibility and low cost as a process fluid. Water-assisted injection moulding (also known as the water-injection technique, WIT) can produce moulded parts with functional cavities more economically than was hitherto possible. It can therefore open up new application areas for thermoplastics. For their part, thermoplastics are being tailored to the requirements of WIT.