When describing many real flows in technical systems, different kinds of viscosities are usually used. In the present article, we discuss how these kinds of viscosities occur and what are relations between them. We show how material constants tensor ⁴C (4^th rank tensor containing 81 terms) transforms strain rate tensor into viscous stresses tensor. Considering the relationship between the strain rate tensors and viscous stresses after the transition from threedimensional to six-dimensional space and using the symmetry properties of the medium, it can be obtained that the number of independent material constants for isotropic fluids decreases to two Lame constants. Taking into account volume expansion rate leads to volume viscosity, which is expressed with that constants. When bulk viscosity is equal to zero there is a model of Newtonian liquid, where Lame constants become proportional to each other. Finally Navier-Stocks equations are written for different expressions of fluid viscosity.