A single mode optical fiber having a core made from silica and less than or equal to about 11 weight % germania and having a maximum relative refractive index Δ1MAX. The optical fiber also has an inner cladding surrounding the core and having a minimum relative refractive index Δ2MIN, a first outer cladding surrounding the inner cladding and a second outer cladding surrounding the first outer cladding. The viscosity at 1650° C. of the second outer cladding minus the viscosity at 1650° C. of the first outer cladding is greater than 0.1e7 Poise, and Δ1MAX>Δ2MIN. The single mode optical fiber may also have an outer cladding surrounding the inner cladding made from silica or SiON. The first outer cladding has a maximum relative refractive index Δ3MAX, and Δ3MAX>Δ2MIN.