# Fabric Material
A fabric material is a variant on an orthotropic material but only exists for the 2D case.
As wth an orthotropic material it is easier to define the inverse of the constitutive relationship
The further (dependent) Poisson's ratio is defined through the relationship
These material properties are defined relative to a material principal directions
A stable material must satisfy the following conditions
Using these relationships leads to the following conditions which apply to the Poisson's ratios