Communicated by the Managing Editors of AIM Dedicated to the memory of Roland Schwänzl MSC: 55P48 55P35 18D50 Keywords: Operads Loop spaces Higher homotopy commutativity Interchange of structuresLet A and B be operads and let X be an object with an A-algebra and a B-algebra structure. These structures are said to interchange if each operation α : X n → X of the A-structure is a homomorphism with respect to the B-structure and vice versa. In this case the combined structure is codified by the tensor product A ⊗ B of the two operads. There is not much known about A ⊗ B in general, because the analysis of the tensor product requires the solution of a tricky word problem. Intuitively one might expect that the tensor product of an E k -operad with an E l -operad (which encode the multiplicative structures of k-fold, respectively l-fold loop spaces) ought to be an E k+l -operad. However, there are easy counterexamples to this naive conjecture. In this paper we essentially solve the word problem for the nullary, unary, and binary operations of the tensor product of arbitrary topological operads and show that the tensor product of a cofibrant E k -operad with a cofibrant E l -operad is an E k+l -operad. It follows that if A i are E ki operads for i = 1, 2, . . . , n, then A 1 ⊗. . .⊗A n is at least an E k1+...+kn operad, i.e. there is an E k1+...+kn -operad C and a map of operads C → A 1 ⊗ . . . ⊗ A n .