A method of making a polyester container having an enhanced level of crystallinity
in the sidewall while maintaining a low level of crystallinity in a thickened base
portion. The container is particularly useful as a refillable container which can
withstand higher caustic wash temperatures and exhibits reduced flavor carryover,
or as a hot-fill container. According to the method, a sidewall-forming section
of a preform is initially expanded, heated to contract and crystallize the same,
and than reexpanded; a base-forming portion of the preform is shielded from the
heat treatment and is expanded either before or after the heat treatment step.
