To any C*-algebra A is associated the simplex Tr(A) consisting of all traces on it. We show that when A is the group C*-algebra of the free group C*(Fn), or when A is the free product of matrix algebras Mn*Mn, the simplex of trace Tr(A) is a Poulsen simplex. This means that the set of extremal traces is dense in Tr(A). The first case is related to certain interesting questions in group theory and dynamics. The second case answers a question by Musat and Rørdam who study this simplex and relate it to factorizable channels in quantum information theory. The talk is based on a joint work with Raz Slutsky and Joav Orovitz.