Two different extrusion-coating qualities of polyethylene, namely LDPE and HDPE, were coated on high-density papers. Differences were observed with respect to their response to storage and low temperature heat treatment. HDPE does not respond to storage at ambient temperature and heat treatment in the same way as LDPE. The LDPE-coating exhibits an increase in the monoclinic crystalline fraction at the paper surface as a result of heat treatment. The nature of this response appears to be a result of adhesion to a paper surface, the properties of this surface, orientation of polymer chains, and chain mobility differences. The increase of the monoclinic fraction is shown to relate to an increase of the mean crystallite thickness and initiation of new crystallites at the paper surface. (C) 2003 Wiley Periodicals, Inc.