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Of course, most of this effect is due to the enhanced value, for the viscoelastic solution, of the width h ( t ) of the mixing layer which en- ters in the definition of all the quantities. As discussed before, another effect induced by polymers is the reduc- tion of small-scale turbulence in the thermal plumes, which leads to an additional enhancement for the heat flux 〈 wT 〉 . Therefore, the Nusselt number for viscoelas- tic turbulence is expected to increase with respect to the Newtonian case when it is observed both as a function of time and as a function of Ra . Indeed, as shown in the inset of Fig. 5, both in the Newtonian and in the viscoelastic cases, Nu ≃ Ra 1 / 2 in agreement with the ultimate state regime (3) but with different coefficients, C$_{N}$ = 0 . 022 ± 0 . 002 and C$_{V E}$ = 0 . 028 ± 0 . 002 respectively, corresponding to an increases of 27%. In conclusion, we have exploited high resolution direct numerical simulations to investigate the effects of poly- mer additives on Rayleigh-Taylor turbulence. There are several advantages in using the present buoyancy-driven turbulence system. The presence of a time evolving mix- ing layer allows us to quantify the acceleration induced by polymers on a natural (nonzero) mean velocity (the mixing layer growth velocity) at fixed buoyancy forc- ing, exactly in the same spirit of usual drag reduction in bounded flows. The relative simple and well under- stood phenomenology of the heat transport (which fol- lows the Kraichnan’s ultimate state regime) allows us to quantify the effects of polymers on the heat transport. While the former feature is specific of the present config- uration, the latter occurs in the bulk of the mixing region and therefore we conjecture that our findings hold in sit- uations more general than the specific setup we studied, as indeed a recent investigation seems to indicate [27]. Moreover, RT turbulence can be realized in laboratory experiments and therefore our results based on numeri- cal simulations of primitive equations are a starting point of the experimental investigation of polymer additive ef- fects on buoyancy-driven turbulent systems. We thank the Cineca Supercomputing Center (Bologna, Italy) for the allocation of computational re- sources.