Static mixer inserts and static mixers incorporating same

A static mixer for liquids or gases includes a housing having a continuous inner surface defining a fluid flow path for liquids or gases, an inlet to the fluid flow path, and an outlet from the fluid flow path, and an insert extending longitudinally through the fluid flow path between the inlet and the outlet. The insert is elastically expansive to exert outwardly directed pressure against the continuous inner surface of the housing. In one embodiment, the insert is hollow and has deflectors dispersed therethroughout and each projecting inwardly into the fluid flow path. In another embodiment, the insert includes a helical deflector extending inwardly into the fluid flow path from the continuous inner surface, and helically about a longitudinal axis of the housing.