Summary: In the framework of a spatially flat FLRW model, we account for dissipative effects in a simple fluid, namely bulk viscosity and matter creation. For an isentropic evolution, we study the wavefront speeds associated with the characteristics of the fluid. With the assumption of a barotropic equation of state, we investigate the consequences on these speeds for power-law behaviour for the scale factor. Our conclusion is that, in contrast to the exponential inflation, the isentropic power-law inflation is compatible with causality, under conditions linking the generalized ‘adiabatic’ index \(\gamma\) to the exponent \(m\) of the power law.