High strength and high modulus fibres have revolutionised the design of lightweight armour, main fibre reinforced ballistic products are: ballistic helmets, vests, blankets and add-on car armour. Modelling of the ballistic properties of multi-layer fibre reinforced armour is still in the development stage, structural models that can be used to describe the penetration of such armour by deformable projectiles, and to design new armour, are not yet available. A simple model has been developed that can be used to calculated the performance of Dyneema armour against deformable bullets and FSPs. Most important in this model is that the number of input values is very small. For calculating the performance of Dyneema UD-based armour only two materials related parameters are required. Four projectile related parameters are needed. For non-deformable projectiles the number reduces to a single material related and two projectile related parameters.