In one embodiment, a pneumatic tire having a built-in sealant layer, before cure, includes an unvulcanized pneumatic tire assembly having an outer circumferential rubber tread and a supporting carcass. A precursor sealant layer is situated between the supporting carcass and an innermost rubber inner liner. The precursor sealant layer includes a non-flowing polyurethane composition that is neither gel-like nor tacky and is self-supporting. The precursor sealant layer, during curing of the unvulcanized pneumatic tire assembly, thermally degrades so as to provide a gel-like and tacky, self-healing polyurethane composition which defines the built-in sealant layer. The resulting tire, with its innermost polyurethane composition, allows for elimination or reduction in blister formation by reducing or elimination the amount of gases typically given off by organoperoxide-butyl based sealant layers, such as when the tire is at its running temperature. Consequently, the thickness of the inner liner may be reduced.