A new technology for making thermoplastic prepreg uses a fibre Impregnated Thermoplastic (FIT) process. Fabric woven from FIT tow prepreg shows a great deal of drapability. A study has been conducted on diaphragm forming technology, using FIT woven fabric made of glass fibres and polyamide. A double curvature mould was used to form hemispherical parts by applying differential pressures across double polyimide diaphragms. Effect of forming rate, lay-up, and cross-section thickness have been investigated. Deformation of diaphragms has been also investigated.