The paper studies the relation between regularity of invariant foliations and Lyapunov exponents of partially hyperbolic diffeomorphisms. The authors introduce the notion of “uniform bounded density” of a foliation in terms of the Radon-Nykodym derivative of the desintegration of the Lebesgue measure along the foliation with respect to the Lebesgue measure on the leaves. Under this assumption the author proves some results for partially hyperbolic diffeomorphisms on the torus \(\mathrm{T}^3\) concerning the rigidity of Lyapunov exponents.