Observational data to reproduce. Different colors indicate different clouds, different symbols indicate different references (circles: AP07; triangles: Anderson et al. 1996, squares: Martin et al. 1992). Top: the “classical” p_V/τ vs. λ_max plot. This panel does not contain the stars without A_V and p_V measurements. Center: comparison of λ_max in extinction with the polarization P₃₅₃/I₃₅₃ in emission. Bottom: the ratio of polarization P₃₅₃/p_max as a function of λ_max.