Rigid, unplasticized poly(vinyl chloride) (PVC-U) sheet products were evaluated comprehensively for the first time with regard to their use in museum showcase construction. The compositions of numerous name brand products (Sintra, Forex, Komatex, Komacel, Celtec, Ex-cel FF, PALIGHT, and ePVC) have been determined using pyrolysis-gas chromatography-mass spectrometry, while their volatile emissions were assessed using modified Oddy tests as well as direct thermal desorption chromatography at elevated temperatures. Despite frequently passing the aggressive conditions of the Oddy test, most premium quality brands were found to release 2-ethylhexyl thioglycolate (2-EHTG), a sulfur-bearing byproduct of a heat stabilizing additive. Importantly, only the economy versions of PVC-U analyzed in this study (Komacel and ePVC) did not contain the sulfur compound. This volatile thioglycolate was shown here using molecular spectroscopies to deposit on and react with copper and silver surfaces. Similarly, lead white pigmented watercolor was blackened by the thioglycolate. Based on these results, alternative materials are recommended for display cases that will contain sulfide-sensitive materials like metals.