A rectangular prism is a cuboid with dimensions x, y, z (length, width, height).
So xyz=32. If we only use integers then, since 32=25, we have the following combinations of dimensions:
(1,1,32), (1,2,16), (1,4,8), (2,2,8), (2,4,4).
If mixed numbers are allowed, there are an infinite number of combinations.