Fabric plays a vital role in determining the engineering behaviour of compacted soils, particularly under unsaturated conditions. Clayey materials compacted dry of optimum moisture content develop an aggregated or "packet" fabric. The presence of aggregations causes the soil to behave in a coarser fashion than would be justified by the grading. This means that the friction angle a (representing the strength component due to net stress) depends on the fabric of the soil. Dry of optimum moisure content, a > ' (the angle of friction in saturated conditions). Similarly, the packet fabric also affects the angle b (representing the strength component due to matric suction). Dry of optimum moisture content, b becomes significantly lower than ' and at low water contents drops to zero. The normal practice for determining the shear strength properties of unsaturated soils (by multi-stage tests in which the suction is increased from an initial low suction state) will result in the packet fabric being destroyed in the first stage of shearing. Therefore, to properly study the shear strength behaviour of unsaturated compacted soils, tests should be performed on the soil in an "as compacted" condition.