Sodium triphosphate, also sodium tripolyphosphate, or tripolyphosphate, is an inorganic compound with formula Na₅P₃O₁₀. It is the sodium salt of the polyphosphate penta-anion, which is the conjugate base of triphosphoric acid. Sodium tripolyphosphate, STPP, is a chemical often used to soak seafood so that it will appear more firm and glossy. It is also known as pentasodium salt or triphosphoric acid.