Or more specific, from the official FINA website:
In regards to the swimwear material, the discussion clarified that there was a broad understanding between the manufacturers and FINA that the rules were not meant and should not be interpreted as limiting the materials to fabrics stricto sensu but that other material could be used, as has already been the case for several years.
FINA confirmed that all the swimsuits approved so far are complying with the specifications.
Read a lot more about this here on SwimNews. And notice that no, you probably cannot just copy Speedo, since they according to SwimNews have registered some 13 patents on their suit.