This project aims to develop tailored non-invasive ventilation (NIV) masks for children in the Paediatric Intensive Care Unit (PICU), to offer suitable masks and to improve the NIV intervention. In the PICU, there is a preference for NIV compared to invasive ventilation, because of complications, such as airway injuries. Their biggest challenge is finding a suitable non-vented NIV mask. They often do not fit well, resulting in too much air leakage and patient-ventilator asynchrony. This increases the breathing effort of the patient, and can lead to NIV failure. The air leakage is often too high, therefore the mask has to be repositioned and tightened to reduce the air leakage. This disturbs the patient and influences the patient’s comfort. The core problem of NIV is the excess of unintentional air leakage. Therefore the main focus lies on reducing air leakage by increasing the fit of the new developed NIV mask. The new masks need to fit patients up till the age of seven, because the available masks do often not fit well. There are no non-vented NIV masks available for patients below one year. An oronasal mask is developed, it is most effective and relatively non-intrusive compared to the other types of non-vented NIV mask. NIV at the PICU can be divided into acute NIV, for which an acute NIV mask will be developed, and extended NIV, for which an ideal NIV mask will be developed. Four concept NIV masks are developed, of which two concepts are selected based on the results of the simulation and most important requirements. The NIV intervention is simulated by ventilating a reanimation mannequin with prototypes of the concepts to determine the effectiveness in terms of air leakage and contact pressure. The two selected concepts shows reduced air leakage compared to commercially available masks. The final design proposal consists of two masks: the Modular Mask, and the Quick Curable Mask. The Quick Curable Mask is developed for patients who require acute NIV. The Modular Mask is developed for patients who need NIV for an extended time. Due to overcrowding at the PICU of Amsterdam UMC there was a shortage of NIV tubes and sensors, it was not responsible to test the masks. Therefore a protocol is written to test the air leakage and evaluate the wearing comfort of the two proposed masks with a test participant after the COVID-19 pandemic. The final design proposal is suitable for NIV at the PICU. A roadmap describes how the two mask can be further developed by the hospital and implemented in the PICU. It consists of the following phases: the optimising phase, the clinical testing phase, the implementing phase, and the redesigning phase.