Degree of crystallinity is controlled by molecular weight
and by the length of time during fabrication that a part is
maintained within the temperature range for rapid
crystallization (307–327°C [585–620°F]). By reheating
fabricated parts according to a standard thermal cycle
(ASTM D4894/4895), relative molecular weights may
be estimated through crystallinity or inherent specific
gravity measurements. In parts with low void contents,
relative molecular weights may be approximated from
apparent specific gravity measurements.