An exemplary fire suppression sprinkler includes a housing (22) that establishes a flow path for discharging fire suppression fluid. A water seat (28) is configured to block the flow path. A polymer seal (30) is supported within the housing (22) and engages the water seat (28) for sealing an interface between the flow path and the water seat (28). A spring member (40) biases the polymer seal (30) into engagement with the water seat (28).