The effects of water vapor on non-oxidative poly(vinyl butyral) functional group decomposition mechanisms are described. Species-specific evolution profiles obtained by mass spectrometric analysis of gases evolved while heating silica, mullite, and alpha-alumina coated with poly(vinyl butyral) binder show that volatile product yields are affected by the presence of water vapor. When water vapor is incorporated into binder burnout atmospheres, acetic acid yields increase and C4H6O yields decrease. Acetic acid yields increased because water vapor interacted with oxide basic sites that otherwise reacted with acetic acid to form carboxylate species. Water vapor also inhibits C4H6O formation, possibly by stabilizing a polar intermediate produced during side group cleavage reactions.