Forms pores that allow passive diffusion of small molecules across the outer membrane. Homotrimer. Forms mixed heterotrimers with OmpC and with PhoE; other mixed heterotrimers with other porins are also probable. Unlike E.coli or S.typhimurium both OmpC and OmpF porins are expressed constitutively, i.e. at both high and low osmolarity, under control of OmpR (at protein level). Belongs to the Gram-negative porin family.