polymer crystal

A crystalline domain usually limited by well-defined boundaries.
  1. Polymer crystals frequently do not display the perfection that is usual for low-molar-mass substances.
  2. Twinned polymer crystals are, sometimes, erroneously referred to as 'crystals'.
  3. Polymer crystals that can be manipulated individually are often called (polymer) single crystals. A single crystal may contain different fold domains.
Purple Book, 1st ed., p. 76 (http://old.iupac.org/publications/books/author/metanomski.html)