Up until recently the only parylene polymers that existed were linear chain polymers, the most common of which are poly(p-xylylene) (parylene N) and poly(chloro-p-xylylene) (parylene C). Both of these polymers have a strong sensitivity towards oxygen and UV light in the presence of oxygen. They are both reactive towards oxygen and subsequently lose mass via chain scission, however cross-linked or networked polymers have much different degradation mechanisms since chain scission is not readily available due to the connectivity of the polymer chains. In this study it is observed that poly(ethynyl-p-xylylene)-co-poly(p-xylylene) (parylene X) is stable to 300 °C in air for one hour after a 1 h post-deposition vacuum anneal at 380 °C, whereas parylene N is stable to just 200 °C for 1 h in air under the same conditions, for 1705 Å and 1826 Å thin films, respectively. After 1000 h at 150 °C in air, parylene X loses little if no film thickness (<0.2%), whereas parylene N loses 7%; however, chain scission is initiated in the parylene X thin films at 362 h. Chain scission is also observed with the birefringence data and in the infrared spectroscopy spectra. The data do not suggest parylene X is more stable than parylene N, but rather its degradation mechanism is much different due to its networked structure, which may have implications for its thermo-mechanical properties. Infrared spectroscopic and ellipsometric data will be presented as a function of time and temperature for both the aforementioned polymers.