There is accident evidence that when a helmetted motorcyclist impacts a deformable steel panel on a car, there may not be any measureable crushing of the polystyrene foam helmet liner. This is especially the case if the helmet shell material is fibreglass(GRP), and if there is double curvature of the helmet shell at the impact site. To investigate this, laboratory impact tests were made in which the headform accelerations, the pressure distributions on both sides of the helmet liner, and the strain distribution in the crushed foam were measure’d..The helmet construction was varied from the standard thermoplastic shell plus polystyrene foam liner to experimental helmets with a much larger ratio of shell stiffness to foam yield stress. Results show that for the standard helmets the load spreading capacity of the shell is limited and in consequence the liner is crushed over a limited area when the helmet impacts a rigid anvil. For the experimental helmet the area of crushed foam is large, and the pressure distribution is uniform across the projected area of the headform, except for high energy impacts when the foam bottoms out. The optimum foam yield stress for impacts on deformable panels is significantly lower than that currently used, particularly when the foam is inside a relatively rigid GRP shell. The consequence of this for European Standards is discussed.