How do I multiply all elements in one collection with all the elements in another collection?

Say I have:

(def s1 [1 2 3 4 5])
(def s2 [1 2 3 4 5])

For every x in s1, I want to multiply it with every y in s2.

To clarify, I basically want the Cartesian product, so I don't think map works here.