Let $A, B$ be unital $C^*$ algebras and $A\star B$ their unital (universal) free product. Assume that $A$ and $B$ are nuclear. When can we say that $A\star B$ is nuclear? I know that it can happen, e.g. $\mathbb{C}^{2}\star \mathbb{C}^{2}=\mathrm{C}^*(\mathbb{Z}_2\star \mathbb{Z}_2)$ is nuclear as $\mathbb{Z}_2\star \mathbb{Z}_2$ is amenable, but on the other hand $\mathrm{C}^*(\mathbb{Z})\star \mathrm{C}^*( \mathbb{Z})=\mathrm{C}^*(F_2)$ is not nuclear.
I would be also interested in an analogous question for the reduced free products.