An appealing inflationary scenario that, for some models, resolves the problem of the flatness of the potential is called ‘warm inflation’. In this model, there is a sizeable production of radiation alongside the inflationary expansion. The inflaton-radiation coupling leads to a significant enhancement of the power spectrum. One needs to consider an imperfect fluid that gives rise to dissipative effects that damp the growth of the fluctuations. However, shear effects can stem from a theory of modified gravity, so they will dominate over the enhancement. I will present a study of the effects of modified gravity on the power spectrum of primordial perturbations.