A mathematical framework for the description of structureless clay behaviour is proposed in this paper. It is based on the observation that there exists a biunique relationship between the radial stress path direction and the compression curve on the specific volume (v = 1 + e)-mean effective stress (σ or p) plane. The projection on the v - σ plane defines the Intrinsic Compression Curve (ICC) of the corresponding radial stress path, which results in infinite possible ICC curves. Following a normalization procedure, a general methodology is presented, which can be applied to any mathematical formulation of the ICC curve. The constants included in this description are called intrinsic properties. This procedure can be easily implemented to anisotropic constitutive models. Its importance is based on the fact that modern constitutive models require a definition of the structureless state, as this state is the limiting reference state of the fully destructured material. In addition, the paper presents a set of correlations for the estimation of the intrinsic properties from the index properties, which helps on the preliminary selection of the material constants.