Penetrative turbulence, which occurs in a convectively unstable fluid layer and penetrates into an adjacent, originally stably stratified layer, is numerically and theoretically analyzed. As example we pick the canonical Rayleigh-Bénard geometry, but now with the bottom plate temperature T b > 4 • C, the top plate temperature T t 4 • C, and the density maximum around T m ≈ 4 • C in between, resulting in penetrative turbulence. Next to the Rayleigh number Ra, the crucial new control parameter as compared to standard Rayleigh-Bénard convection is the density inversion parameter θ m ≡ (T m − T t )/(T b − T t ). The crucial response parameters are the relative mean midheight temperature θ c and the overall heat transfer (i.e., the Nusselt number Nu). We numerically show (for Ra up to 10 10 ) and theoretically derive that θ c (θ m ) and Nu(θ m )/Nu(0) are universally (i.e., independently of Ra) determined only by the density inversion parameter θ m and succeed to derive these universal dependences. In particular, θ c (θ m ) = (1 + θ 2 m )/2, which holds for θ m below a Ra-dependent critical value, beyond which θ c (θ m ) sharply decreases and drops down to θ c = 1/2 at θ m = θ m,c . This critical density inversion parameter θ m,c can be precisely predicted by a linear stability analysis. Finally, we numerically identify and discuss rare transitions between different turbulent flow states for large θ m .