A sheeting is provided for use with a fluid processing cassette having a valve station with a plurality of fluid flow ports. The sheeting has a generally flexible layer and a biasing member associated with the layer. The sheeting is attached to the cassette such that the biasing member is received within the valve station. The cassette may be used with a fluid processing system having a valve actuator with a piston that is aligned with the cassette during use. In an extended position, the piston presses the sheeting against the port to prevent fluid flow through the valve station. When the piston moves from the extended position to a retracted position, it allows the sheeting to uncover the port, thereby allowing fluid flow through the valve station. The biasing member assists in displacing the sheeting from the port when the piston moves to the retracted position.