The universal cluster ICM density profile. Left: scaled density profiles of the SZE-selected clusters (grey points), overplotted with the best-fitting GNFW model with free evolution and mass dependence: ρ_gas/ρ₅₀₀(R/R₅₀₀)∝E(z)^α_z M^α_M with α_z = 2.09 ± 0.02 and α_M = 0.22 ± 0.01 (orange line). The model includes a radially varying intrinsic scatter term (orange envelope). Right: comparison of the best-fitting model, defined on the SZE-selected sample, to the best-fitting model for the X-ray-selected REXCESS sample (light blue). Here, the points with error bars are the REXCESS sample.