This work presents a detailed study on cross-linking in polydimethylsiloxane (PDMS) and its manifestation in terahertz (THz) absorption characteristics. The characteristics, acquired via THz time-domain spectroscopy, are shown to depend upon the curing agent mass fractions as well as the curing temperatures, times, and environments. Of particular note is the increased THz absorption seen by curing at high temperatures, which leads to increased cross-linking and the promotion of primary and secondary post-curing reactions. Such findings can lay the foundation for the use of PDMS in emerging THz microfluidic platforms.