Physical constants are usually treated as fundamental givens, derived quantities, empirical parameters, or effective coefficients within established theories. This paper proposes a further category: closure-synthetic constants. A closure-synthetic constant is not produced by arbitrary algebraic combination of known constants. It becomes admissible only when a closure condition stabilizes a new invariant within a specified domain, operator structure, boundary condition, or regime. The paper distinguishes seed, generative, derived, transition, and closure-synthetic constants, arguing that synthetic constants become meaningful only when they satisfy dimensional coherence, closure necessity, domain specificity, invariant stability, and functional consequence. Two worked examples are developed: CACO = (pi - 3) /3, interpreted within the Unified Coherence Closure Framework as a candidate baryonic appearance constant, and CEI, an electromagnetic-information closure threshold governing the preservation of informational distinction through electromagnetic propagation. A secondary gravitational-thermodynamic candidate is also discussed. The central claim is that constants are invariant residues of closure: some are primitive, some are derived, and some may be generated when new closure regimes stabilize relations not visible in the original domain. Keywords closure synthesis; synthetic constants; physical constants; derived constants; transition constants; baryonic matter; dark sector; electromagnetic information; UCCF; invariant residues; closure theory
Philip Lilien (Fri,) studied this question.