Apparatus for multiplying layers in a composite polymer stream includes an intermediate section having open conduits sandwiched between housing sections that close the conduits. The conduits have respective first stages separated by a first blade extending to a first face, and respective second stages separated by a second blade extending to a second face. The first stages separate the stream into sub-streams and compress and shift the sub-streams in a first dimension, whereas the second stages shift the sub-streams in a second dimension. In order to maintain a constant cross-sectional area of the sub-streams, the housing sections may be provided with complementary open channels. The apparatus can be used to multiply layers which are side-by-side or one-over-another by changing orientation in the direction of flow.