To better understand the mechanisms underlying thermal post-processing, monomer conversions were tracked via Fourier transform infrared spectroscopy (FTIR) as a function of heat treatment conditions (Fig. and fig. ). As-printed specimens showed nearly complete acrylate conversion in both 405 nm-and 365 nm-cured regions. In contrast, roughly 50% epoxide conversion was achieved in 365 nm-cured regions, while no measurable epoxide conversion was observable in the regions exposed to 405 nm light (Fig. ). At higher thermal treatment temperatures and longer hold times, epoxide conversion increased in both visible-and UV-exposed regions, though UV-exposed regions always maintained higher epoxide conversions for any given thermal treatment. Notably, regions exposed to visible light remained soluble, even at epoxide conversion percentages that exceeded those of insoluble UV-exposed samples, indicating dissolution behavior cannot be fully explained in terms of epoxide conversion. We hypothesized that this difference in solubility occurs because purely thermal curing results in lower crosslink densities due to the different mechanisms for light-and heat-driven polymerization. Specifically, reaction conditions during UV light exposure favor chain propagation, while thermally initiated polymerization favors chain transfer and termination . Because these side reactions can result in the termination of propagating chains or the formation of cyclic oligomers, thermally induced polymerization generates lower crosslink density. Thus, the post-printing thermal treatment of the visible-cured materials results in reduced solvent resistance compared to UV-cured regions, even at the same level of epoxide conversion. While lower crosslink density would be undesirable for the final printed product, it is highly beneficial in the development of dissolvable support structures. DMA experiments on printed, thermally cured samples yielded tan(δ) curves with distinct differences in mechanical response near the glass transition temperature (Tg) of the hybrid material, consistent with the hypothesized differences in polymer network structure (Fig. and Fig. ). Tan(δ) is equal to the ratio of the loss modulus (dissipated energy) to the storage modulus (elastically stored energy) in a viscoelastic material undergoing oscillatory strain. Physically, low values of tan(δ) correspond to highly elastic materials, while high values of tan(δ) indicate viscous, energy-dissipating behavior. 405 nm-light-exposed samples show a distinct peak in tan(δ) at approximately 120°C, corresponding with the material's Tg, while 365 nm-exposed samples show this transition a few degrees higher, with significantly reduced peak magnitude. The reduced tan(δ) peak height corresponds to the greater elastic character and lower chain mobility of the UVexposed material above its Tg, indicating an increased crosslink density relative to the visibleexposed material. The higher mobility of visible-exposed polymer at higher temperatures was also reflected in its greater deflection from plastic flow during DMA (Fig. ). Additional dissolution experiments supporting the crosslink density hypothesis are detailed in Figure .