Glazing unit comprising a transparent, especially glass, substrate equipped with an antireflection coating, which coating comprises at least one film of a porous material essentially comprising silicon, oxygen, carbon and possibly hydrogen, in which the atomic proportion PC of carbon, relative to the sum of the atomic contributions of silicon, oxygen and carbon, varies locally in the thickness direction of the film, from a first surface to a second surface thereof: increasing between a first minimum value PCmin1 and a maximum value PCmax, the ratio of said maximum value PCmax to said first minimum value PCmin1 being at least 1.2, the proportion of carbon then decreasing, between said maximum value PCmax and a second minimum value PCmin2, the ratio of said maximum value PCmax to said second minimum value PCmin2 being at least 1.2.