The reciprocal of viscosity is fluidity, usually symbolised by φ (=1/μ), measured in reciprocal poise (cm·s/g), sometimes called the rhe.

Fluidity is seldom used in engineering practice.

Fluidity is used in a number of different scientific areas including geophysical fluid dynamics, computational fluid dynamics, ocean modelling and mantle convection.

It uses a finite element/control volume method which allows arbitrary movement of the mesh with time dependent problems, allowing mesh resolution to increase or decrease locally according to the current simulated state.

It has a wide range of element choices including mixed formulations.