Cystic fibrosis (CF) is associated with chronic progressive lung disease that may lead to respiratory failure.Bi-Phasic Cuirass Ventilation (BPCV) is a form of non-invasive respiratory support, which can provide negative pressure ventilation as well as high frequency chest wall oscillations and cough mode.The standard therapy for CF patients to release mucous is treatment by a physiotherapist. In this study we will compare the effect of BPCV with regular physiotherapy by full pulmonary function testing prior and post treatment.