As the demand for prematur infant incubators are constantly high, especially in Indonesia as the fifth-ranked country of the world's most prematur baby (675,700 babies per year), the concept of grashof incubator has been developed to fulfill the needs of Indonesian citizens. As the demand grows, the need to solve twin prematur babies' problem has been emerging ever since. The designation of Twin Baby Incubator follows the basic concept of existing grashof incubator with bigger volume as a mean to include two babies at the same time. Using 3D modelling software, the product design development mainly focuses on adapting the current functionalities of grashof incubator into the twin grashof baby incubator, such as keeping the babies' cabin temperature at 33°C-35°C by allowing natural convention and natural circulation to occur. Beside the main functionalities, the design also focuses on ergonomic aspects as well as material consideration as a mean to improve usability and efficiency. Furthermore, a research was conducted to make sure that the temperature of 33°C-35°C can be achieved regardless bigger volume of babies' cabin. As the design follows the concept of grashof incubator, the main components are light bulbs as the main heater and digital thermostat as a temperature controller. DS18B20 sensors are used to measure temperature where they are being placed at ten different points of measurements, and DHT22 sensor is placed to measure the level of humidity. The expected results of the research are the capability of developed twin incubator to achieve mandatory temperature, as mentioned above, inside the cabin using 4 × 15 W light bulbs as a heater.