High performance fibre reinforced polymer composites are made by embedding high strength/modulus fibres in a polymeric matrix. They are a class of materials that owe its success to the impressive specific mechanical properties with respect to metals. In many weight-sensitive applications, where high mechanical properties and low mass are required, properties per unit of mass are more important than absolute properties and further weight reduction is desirable. A route to reach this goal could be the controlled induction of porosity into the polymeric matrix, while still ensuring load transfer to the reinforcing fibres and fibre protection from the environment. Cellular lightweight fibre reinforced composites (CellFRC) were prepared embedding gas bubbles of controlled size within a high performance thermoplastic matrix reinforced with continuous fibres. Pores were induced after the composite was first saturated with CO2 and then foamed by using an “in situ” foaming/shaping technology based on compression moulding with adjustable mould cavities. The presence of micro- or submicro-sized cells in the new CellFRC reduced the apparent density of the structure and led to significant improvements of its impact properties. Both structural and functional performances were further improved through the use of a platelet-like nanofiller (Expanded Graphite) dispersed into the matrix.