Polystyrene aggregate concrete is one of many lightweight, low strength materials with good energy-absorbing characteristics. However, due to poor workability and a susceptibility to segregation, quality control is difficult during manufacture. This Paper describes the procedures adopted for the mix design and casting of concretes containing 40, 50 and 60 vol.-% (corresponding to specific densities of 0·8, 1·0 and 1·2 respectively) of beaded polystyrene aggregate. Strength and density were controlled by varying the mix proportions. Stress-strain relationships are given, and the compressive strength is shown to vary approximately linearly with density. Modifications to Pauw's equation for the determination of Young's modulus are considered.